GEOLOGY and GROUND-WATER RESOURCES of the ISLAND of MOLOKAI, Hawall

J '"'" ~ ...,.,, • - ;- • -:·-- __, - .. ~ ~ .:..; ,.,;: -~·t: '!' ; ... ~--

GEOLOGY AND GROUND-WATER RESOURCES OF THE ISLAND OF MOLOKAI, HAWAll

H. T. STEARNS AND G. A. MACDONALD

BULLETIN 11 HAWAII DIVISION OF HYDROGRAPHY 1947 BULLETINS OF THE DIVISION OF HYDROGRAPHY TERRITORY OF HAWAII

* 1. GEOLOGY AND OROUND-WATER RESOURCES OF THE ISLAJ.\'D OF OAHU, HAW All. By Harold T. Stearns and Knute N. Vaksvik. 1935.

* 2. GEOLOGIC MAP AND GUIDE OF THE ISLAND OF OAHU, HAWAil. By Harold T. Stearns. 1939.

* 3. ANNOTATED BIBLIOGRAPHY AND INDEX OF GEOLOGY AND WATER SpPPLY OF THE ISLAND OF OAHU, HAWAII. By Norah D. Stearns. 1935.

* 4. RECORDS OF THE DRILLED WELLS ON THE ISLAl:U> OF OAHU, HAWAll. By Harold T. Stearns and Knute N. Vaksvik. 1938.

5. SUPPLEMENT TO THE GEOLOGY AND GROU?-.'1>-WATER RESOURCES OF THE ISLAND OF OAHU, HAWAII. By Harold T. Stearns. Includes chapters on geo physical investigations by Joel H. Swartz, and petrography by Gordon A. Macdonald. 1940.

6. GEOLOGY AND GROUND-WATER RESOURCES OF THE ISLANDS OF LANAI AND KAHOOLAWE, fuWAil. By Harold T. Stearns. Includes chapters on geophysical investigations by Joel H. Swartz, and petrography by Gordon A. Macdonald. 1940.

* 7. GEOLOGY AND GROUND-WATER RESOURCES OF THE ISLAND OF MAUI, HAWAII. By Harold T. Stearns and Gordon A. Macdonald, 1942.

8. GEOLOGY OF THE IlAWAIIAN ISLANDS. By H. T. Stearns. 1940.

9. GEOLOGY AND GROUND-WATER. RESOURCES OF THE ISLAND OF HAWAII. By Harold T. Stearns and Gordon A. Macdonald. 1946.

10, BIBLIOGRAPHY OF THE GEOLOGY Al).'1) GROUND-WATER RESOURCES OF THE ISLA1)."1l OF HAWAII. Annotated and indexed. By Gordon A. M.acdonald. 1947.

11. GEOLOGY AND GROUND-WATER RESODRCES OF THE ISLAND OF MOLOKAI, HAWAII. By Harold T. Stearns and Gordon .A.. Macdonald. 1047.

TOPOGRAPHIC MAP OF THE ISLAND OF HAWAII, scale 1:125,000, contour in terval 250 feet, size 44 x 49 inches, price $1.00, for sale by the Survey Department, Territodal Ofilce Building, Honolulu 2, T. H.

* Out of print. Plate 3. Aerial Yiew of :.\Iololrni from the east, sho,Ying the great northern diff 011 the right \Yith Kalaupapa Peninsula at its foot, in the right foreground the amphithenter-headed IInlawa Yalle~·. and in the middle distaiwe the great nillers of ,Yailau alld Pelekunn. the lwads of \Yhkh mark the positiou of the uuciP1it (·aldera. Photo l>y r. S. Army Air For<:e. TERRITORY OF HAWAII I.:-.GRAJ\1 J\1. :S'l'.·\I.:-.HACK, Gorernor A. LESTER MARKS, Gommis8ioner of Public Lands DIVISION OF HYDROGRAPHY MAX H, CARSOX, Chief Hydrographer

BULLETIN 11

GEOLOGY AND GROUND-WATER RESO·URCES OF THE ISLAND OF MOLOKAI, HAW All

BY HAROLD T. STEARNS Former District Geologist, U. S. Geological Survey

AND GORDON A. MACDONALD District Geologist, U. S. Geological Survey

Prepared in cooperation with the Geological Survey, United States Department of the Interior

Printed in the Territory of Hawaii, rnited States of America; April 1947 Distributed by the U. S. (;eoJogieal Sm·,·py, 333 Federal Bldg.. Honolulu, Hawaii CONTENTS PAGE Abstract 1 PART 1. GEOLOGY OF 1\foLOKAI, by H. T. Stearns...... 3 Introduction ...... 3 Location and area...... 3 Historical sketch ...... 3 Population and industries...... 5 History and purpose of the investigation...... 6 Acknowledgments ...... 7 Previous investigations ...... 7 Geomorphology ...... 11 Original form of East Molokai...... 11 Origin of the Hoolehua Plain...... 13 Emerged and submerged shureli11es...... 13 Living reef ...... 15 General character, age, and water-bearing properties of the rocks...... 15 Straligravllk lable of Molokai ...... Facing page 16 Tertiary volcanic rocks...... 16 East Molokai volcanic series...... 16 Lower member ...... 16 Lava flows ...... 16 Cones and vitric tuff deposits...... 17 Intrusives ...... 17 Caldera complex ...... 19 Upper member ...... 22 Lava flows ...... 22 Cones and bulbous domes...... 23 Erosional unconformity ...... 23 West Molokai volcanic series . . 2R Distribution ...... 23 Character and structure...... 24 Cones and vitric tuff deposits...... 24 Dikes ...... 25 Quaternary volcanic rocks...... 25 Kalaupapa basalt ...... 25 Tuff of Mokuhooniki cone...... 26 Sedimentary rocks ...... 26 Calcareous marine deoosits...... 26 Consolidated earthy deposits...... 27 Consolidated dunes ...... 28 Unconsolidated dunes ...... 28 Beach deposits ...... 29 Unconsolidated earthy deposits...... 29 Geologic structure ...... 29 East Molokai ...... 29 West Molokai ...... 31 Geologic history ...... 31 Road metal ...... 35

iii CONTENTS

PAGE

PART 2. GROUND-WATKli RESOURCES OF :rtlOLOii:AI, by G. A. Macdonald .... 37 Climate ...... · · · · · · · · · · · · · · · · · · · · · · · · ·· · · · · · · · · · · · · · · · · · · · · · · · · 37 Temperature, wind, and humidity...... 37 Rainfall ...... 37 Surface water ...... 47 Meyer Lake ...... 49 Domestic water supplies...... _...... 50 Basal ground water...... 53 General features ...... 53 Basal Springs ...... 56 Wells 57 Perched ground water ...... 67 General f Pa tnrPR ...... 67 Perched springs ...... 67 Tunnels developing perched ground water...... 71 Water confined at high levels by dikes ...... 72 Quality of ground water...... 77 Use of water from the large windward valleys ...... 79 Future developments ...... 84 PART 3. PETROGRAPHY OF l\foLOKAI, by G. A. Macdonald...... 89 Abstract ...... ·...... 89 Introduction ...... 89 Previous investigations ...... 90 Tertiary volcanic rocks ...... 92 East Molokai volcanic series...... 92 Lower member ...... 92 General characteristics ...... 92 Olivine basalts ...... 95 Basalts ...... 97 Picrite-basalts ...... 98 Upper member ...... 99 General features ...... 99 Oligoclase andesites ...... 99 Andesine andesites ...... 103 Trachytes ...... 103 Inclusions in lavas...... 104 Intrusive rocks ...... 104 West Molokai volcanic series...... 105 General features ...... 105 Olivine basalts ...... 105 l'icrite-basalts ...... 107 Basalts ...... 107 Hypersthene-bearing basalts ...... 108 Quaternary volcanic rocks...... 109 Kalaupapa basalt ...... 109 Tuff of l\fokuhooniki cone...... 109 Magmatic differentiation ...... 109 ILLUSTR.A.TIOXS

PLATE FACINfl PACE 1. Geologic and topographic map of Molokai. sho,ving wells, springs, and tunnels ...... In pocket 2. Map of Molokai showing principal roads and points of geologic inter- est, with a descriptive text...... In pocket 3. Aerial view of Molokai from the east...... Frontispiece 4. Kalaupapa Peninsula, and the northern cliff of :Molokai ...... 14 5. A-Aerial view of Pelekunu Valley. B-Boulders rounded by wave action during a high stand of the sea...... 15

6. A-Southern slope of East Molokai. B-Armored desert 011 ·west ~Iolokai ...... 20 7. A-Head of Kamalo Gulch, East Molokai. B-Sea cliff near :Mokio Point, West Molokai...... 21 8. A-Kalaupapa Peninsula from Waikolu Valley. B-Reef of the 25- foot stand of the sea, near Kaunakakai...... 26 9. A-Beach rock, near Halena, West Molokai. B-Terraces at mouth of Waileia Valley...... 27 10. A-Lithified sand dunes near Ilio Point, West ::Vlolokai. B-Lithified sand dunes near Moomomi Beach...... 46 11. Aerial view of Halawa Valley, East Molokai...... 47 12. A-Fault scarps and graben, on eastern slope of West Molokai. B- J\Ieyer Lake ...... 74 13. A-Aerial view of Papalaua Valley. B-Ohialele Stream, in Waikolu Valley ...... 75 14. A-East wall of Kamalo Gulch, showing andesite dome and flow. B- East Molokai from Kaunakakai wharf...... 98 15. A-Aa anct pahoehoe lavas near Halena, West Molokai. B-.Andesite resting on soil near Waialua, East Molokai...... 99

V ILLUSTRATIONS

FTOURE PAGE l. Land utilization map of Molokai ...... 4 2. Map of Molokai, showing geomorphic areas ...... 10

3. Profiles through the northern coast of East Molokai ...... 12

4. Dfagram of dike showing arched vesicle bands ...... 18 5. Stage drawings illustrating the development of Molokai...... 32 6. Map of Molokai, showing distribution of rainfall and rain gages .... . 39

7. Diagrams illustrating monthly distribution of rainfall at eight stations on Molokai ...... 41 8. Duration-discharge cur,es for Pulena and Pelekunu streams ...... 48 9. Intensity-frequency curve for Halawa Stream...... 49 10. Map of Molokai, showing main pipelines supplying domestic water .. 51

11. Diagram illustrating the Ghyben-Herzberg principle ...... 53 12. Graph showing water-level fluctuations in Maui-type well 1 and dug well 42 ...... 62 13. Graph showing water-level fluctuations in Maui-type well 6 aml tesl- 1 boring 1 ...... 63 14. Map of Kaunakakai and vicinity, showing positions of abandoned drilled wells ...... 66 15. Map of Molokai, showing ground-water areas...... 68 16. Section across East :Molokai, showing ground-water conditions ...... 76 17. Map showing proposed tunnel routes from windward valleys to dry leeward areas ...... 80 18. Map of West Molokai showing late lava flows...... 106

vi GEOLOGY AND GROUND-WATER RESOURCES OF THE ISLAND OF MOLOKAI, HAWAII

H. T. STEARNS AND G. A. MACDONALD

ABSTRACT The island of Molokai is the fifth largest of the Hawaiian Islands, with an area of 260 square miles. It lies 25 miles southeast of Oahu, and 8.5 miles northwest of Maui. It consists of two principal parts, each a major volcanic mountain. East Molokai rises to 4,970 feet altitude. It is built largely of basaHk lavas, with a thin cap of andesites and a little trachyte. The volcanic rocks of East Molokai are named the East Molokai volcanic series, the basaltic part being separated as the lower member of the series, and the andesites and trachytes as the upper member. Large cinder cones and bulbous domes are associated with the lavas of the upper member. Thin beds of ash are present locally in both members. The lavas of the lower member are cut by innumer able dikes lying in two major rift zones trending eastward and northwestward. A large caldera, more than 4 miles long, and a smaller pit 0.8 mile across existed near the summit of the volcano. The rocks formed in and under the caldera are ·separated on plate 1 as the caldera complex. Stream erosion has cut large amphitheater-headed valleys into the northern coast of East Molokai, exposing the dikes and the caldera complex. West Molokai is lower than East Molokai, rising to 1,380 feet altitude. It was built by hasaltic lavas erupted along rift zones trending southwestward and northwestward. Many of the flows were unusually fluid. The volcanic rocks of West Molokai Volcano are named the West Molokai volcanic series. Along its eastern side, the mountain is broken by a series of faults along which its east ern edge has been dropped downward. West Molokai Volcano became extinct earlier than East Molokai Volcano, and its flank is partly buried beneath lavas of East Molokai. Both volcanic mountains were built upward from the sea floor probably during Tertiary time. Following the close of volcanic activity stream erosion cut large canyons on East Molokai, but accomplished much less on drier West Molokai. Marine erosion attacked both parts of the island, producing high sea-cliffs on the windward coast. In late Tertiary or early Pleistocene time tlie island was submerged to a level at least 560 feet above the present shore line, then reemerged. Later shifts of sea level, probably partly resulting from Pleistocene glaciation and deglaciation, ranged from 300 feet below to 100 feet or more above present sea level. Marine deposH:s uu the southern slope extend to an altitude of at least 200 feet. Eruption of the Kalaupapa basalt built a small lava cone at the foot of the northern cliff, forming Kalaupapa penin sula ; and a small submarine eruption off the eastern end of Molokai built the Mokuhooniki tuff cone, the fragments of which now form Hooniki and Kanaha

1 2 l\IOLOKAI

Islands. Deposition of marine and fluviatile sediments has built a series of narrow flats close to sea-level along the southern coast. Nearly the entire island is underlain. close to sea level, by ground water of the basal zone of saturation. Beneath ,vest Molokai, the Hoolehua Plain between West and East Molokai, and the southern coastal area of East )lolokai, the basal water is brackish. Beneath much of East Molokai, fresh basal water is obtainable. Small amounts of fresh water are perched at high levels in East Molokai by thln poorly permeable ash l>etl:s. Fresh water is con fined at high levels in permeable compartments between poorly, permeable dikes in the rift zones of East Molokai, and can be developed by tunnels. Projects to bring the abundant surface and ground water of the large wind ward valleys to the Hoolehua Plain are described. Future developments are suggested. All wells and water-development tunnels are described in tables. In the section on Petrography the Yukauic rocks are described, and chemical analyses are listed. PART 1. GEOLOGY OF :MOLOKAI by H. T. STEARNS

INTRODUCTION LOCATION AND AREA.-The island of Molokai, County of Maui, is separated from Oahu by Kaiwi Channel, 25 miles wide, from Maui by Pailolo Channel, 8.5 miles wide, and from Lanai by Kalohi Chan nel, 9 miles wide. ( See insert map, plate 1.) Its form is shown by the topographic contours in plate 1, its appearance as seen from the east in the frontispiece, and its relief by plate 2. It is 38 miles long, 10 miles wide, and has an area of 260 square miles. The highest point is Kamakou Peak on East Molokai Volcano, altitude 4,970 feet. The distribution of the area on Molokai with respect to ele Yation follows:

Distribution of area of Molokai with respect to elevationl Altitude in feet Area in square miles Percent 0-500 97.0 37.3 500-1000 66.0 25.4 1000-2000 50.6 19.5 2000-3000 30.1 11.6 3000-4000 13.8 5.3 4000-4970 2.5 .9

260.0 100.0

HISTORICAL SKETCH 2 .-Captain Cook sighted Molokai on Novem

ber 261 1778, but did not land. He called the island Morotai. The Rev. R. H. Hitchcock and wife were the first resident missionaries. They settled at Kaluaaha on November 7, 1832. R. "'\V. )1eyer, who arrived from Germany in the early forties, settled at Kalae and started the cattle industry with longhorns. He also raised sugar and operated a small horse-motivated sugar mill. Between 1870 and 1900 sugar mills were operated at Mounui and Kamalo. By 1900 all sugar production ceased. Kamehameha V bought large tracts of land on Molokai for a country estate. Charles R. Bishop inherited these lands through his wife Bernice Pauahi Bishop. In 1897 the Bishop Estate sold the central and western holdings of about 70,000 acres to A. "'\V. Carter,

1 Wentworth, C. K., Physical geography and geology: in Hawaii Terr. Planning Board First Progress Rept., p. 15, 1939. 2 The entire sketch is abstracted from Judd, G. P. IV, Puleoo, the story of )!olokai: 28 pp., Honolulu, 1936.

3 0 2 3 4 Smiles Kama lo ~~~~,...,...,....,.EXPLANATION I Ranch 111111111111111111111111111111111 Forest Pineapple Homestead Figure 1. Map of Molokai showing land utilization in 1937. (After pl. 36, Hawaii Terr. Plan. Bd., 1st Progress Rept., 1939.) INTRODUCTION 5 A. S. Hartwell, ,v. R. Castle, and J. B. Castle for $150,000. They formed the Molokai Ranch and promoted the American Sugar Co. The American Sugar Co. leased 30,000 additional acres of land, and began operations in 1898. A mole half a mile long was con structed at Kaunakakai, a railroad from the mole to the Hoolehua Plain was built and put in operation, 500 acres of cane were planted, 8 miles of irrigation ditches dug, wells were drilled near Kauna kakai and steam-driven pumping equipment with a capacity of 10,000,000 gallons of water daily was installed. By 1900 the thin lay er of fresh water had been pumped out and the wells were yielding only salt water which soon killed the cane. The whole plantation f:tilPcl ,HRm::i.1ly hf'fore the mill had been erected. The population fell from about 6,000 in 1834 to 1,006 in 1910. About 1918 it was discovered that pineapple could be raised on Molokai and a great boom developed in this product. The popula tion climbed to 5,677 by 1935 and shifted from the wet windward areas and eastern end to the dry western part of the island. Cali fornia Packing Corporation and Libby, McNeil!, & Libby soon took over most of the pineapple industry either leasing the land or paying a fixed amount per ton for pineapples ra.iRf>il. In 1!l3n thei;.e two plantations occupied 11,000 acres with a capital investment of about $2,500,000. A wharf was built at Kolo for shipment of pine avvles frum the Mauna Loa section. The Hawaiian Homes Commission, soon after they were formed in 1920, opened the Hoolehua homesteads for entry. POPULATION AND INDUSTRIES.-Molokai had a population of 5,341 in 1940. Kaunakakai is the principal town and port. The island is reached by interisland steamers and planes. The main airport is on the Hoolehua Plain, an isthmus of land connecting East and "'\Vest Molokai. The Territorial leper colony, population 447 in 1940, occupies only 4.j square miles of the island on Kalaupapa Peninsula, a low peninsula separated from the major part of the island by a high cliff ( pl. 4). The chief industries are the production of pineapple and livestock. Formerly 200 to 300 tons of algaroba honey were produced annually by the Molokai Ranch, Ltd., but about 1935 it became uneconomical to produce honey. About 13,253 acres of land were used for the growing of pineapples in 1945, distributed as follows: Libby, Mc Neill, & Libby 8,453 acres and California Packing Corporation 4,800 acres. The pineapples are canned in Honolulu. About 76,200 acres are used for grazing. The two largest ranches are Molokai Ranch on the western end of the island, with 53,372 acres; and Puuohoku Ranch on the eastern end, with 13,891 acres. 6 l\lOLOKAI

Ahont 6,150 acres of the Hoolehua Plain have been settled by Hawaiian homesteaders. Part of this land is used for truck garden ing but the chief crop is pineapples, grown under contract to Libby, McNeill & Libby and California Packing Corporation. The Hoole hua Plain contains about 28,000 acres of land covered ·with deep soil. The climate is semi-arid and in many years is too dry for truck gardening. The U. S. Bureau of Reclamation has surveyed a pro ject to irrigate 12,000 acres of this land with water conducted through a series of tunnels 18.3 miles long from the windward wet valleys of East Molokai.3 The development of the island has been greatly retarded by the lack of wntP.r in the inhabitated areas. The Molokai projf'd, if constructed, would greatly change the economy of the island. HISTORY AND PURPOSE OF THE INVESTIGATION.-This report repre sents the completion of another unit in the systematic study of the geology and ground-water resources of the Hawaiian Islands by the Geological Survey, U. 8. Department of the Interior, in cooper ation with the Division of Hydrography, Territory of Hawaii. The study was started by H. T. Stearns in 1935 to furnish the basic geologic and hydr-0logic data for the investigation started subse quently by the Bureau of Reclamation as the Molokai irrigation project. During this period, camps were established in the difficultly accessible windward valleys with the aid of the Civilian Conserva tion Corps, and every tributary of Wailau, Pelekunu and Haupu streams was mapped. Part of vVest Molokai, ,vaikolu Valley, and the Kalaupapa Peninsula were mapped also at this time. The field work lasted from June 1 to September 13, 1935. D. John Ceder strom traversed the leeward valleys of East Molokai during this same period and made a collection of rock specimens for micro scopic study. In 1938 and 1939 Stearn8 investigated water supplies for Kauna kakai and adjacent areas at the request of the Board of Super visors, Maui County. In 1939 a Maui-type well was started, at an altitude of 301 feet, in Kaunakakai Gulch by the Works Progress Administration, but was stopped at a depth of 30 feet because of the lack of excavating equipment. In August, 1939, a test hole was drilled in this shaft at the expense of the County of Maui. It demon strated clearly the presence of potable water at this site. Another test hole was drilled by the Geological Survey' near the Hoolehua airfield in 1938. G. R. Maccarthy, of the Geological Survey, made a resistivity survey of the isthmus area in 1939. G. A. Macdonald

s Howell, Hugh, Final report on water-supply studies, Hawaii FP. No. 45, Island of Molokai (abridged), 61 pp., Honolulu, 1938. INTRODrCTION 7 spent from September 12 to October 18, 1945, completing the geo logic mapping and ground-water investigations on the leeward slopes of East Molokai and the eastern part of West Molokai. ( See key map, pl. 1.) AcKNOWLEDGMENTs.-The Geological Survey is greatly indebted to the Molokai Ranch, Ltd., especially to Mr. George P. Cooke, manager, for splendid cooperation thruuglwut the work. Libby, 1\lc Neill, & Libby likewise cooperated generously in the resistivity sur vey of West Molokai. Messrs. Herbert Wilson, Mitchell Pauole and Solomon Hanakeawe have rendered valuable assistance by measur ing certain observation wells monthly. Mr. Julian Yates, executive officer of the Hawaiian Homes Commission, supplied helpfnl in formation. The Department of Agriculture of the Territory of Hawaii co operated by furnishing boat transportation and guides for the work in the windward canyons. Numerous local residents assisted in various ways, especially Messrs. Charles Morris, George Apana, Raymond Duvauchelle, F. N. Tollefson, Charles Kamali, Daniel Naki, Basilio Agcaoili, and George Davis. The Hawaiian Sugar Plauters Association generously permitted the use of a house at their Mapulehu experiment station, and Mr. George Otsuka sup plied information regarding the wells and tunnel at Mapulehu. Mr. vV. F. Feldwisch, of the U. S. Weather Bureau, furnished data on rainfall. Mr. M. H. Carson, of the U. S. Geological Survey, furnished data on stream and spring discharge. Messrs. Howard Leak and H. W. Beardin aided in measuring the dug wells. Mrs. Ethel U. McAfee edited the report and Mr. J. Y. Nitta pre pared the illustrations. PREVIOUS INVESTIGATIOxs.-Dana4 recognized the fact that Molo kai hau been built by two volcanoes and suggested that the great windward cliff might be a fault scarp. Lindgren5 made the first field study of the island. He recognized that ·west Molokai Volcano became extinct earlier than East Molokai Volcano. He described the cliffs on the eastern side of West Molokai and the great wind ward cliff of B::ist Molokui as due to faulting. He thought, erron eously, that Kalaupapa Peninsula was a part of a sunken block still above sea level. He reported boulders of a coarse-grained intrusive in Wailau Valley. He described in detail the water resources, and recognized that the basal water is floating on salt water, and sug gested the construction of tunnels to bring water fr9m the ,viud-

4 Dana, J. D., Characteristics of volcanoes: p. 290, New York, 1890. • Lindgren, Waldemar, The water resources of :Molokai, Hawaiian Islands : U. S. Geological Survey, Water-Supply Paper 77, 62 pp., 1903. 8 l\IOLOKAI ward valleys to the dry leeward slopes. Powers6 noted the presence of trachyte on East Molokai and that Kalaupapa is a young cone of olivine basalt. Bigelow and Stewart7 reported on the water supply and development of power at Kalaupapa. Wentworth8 de scribed in detail the sand dunes on West Molokai and noted three different ages of dunes. Hinds9 recognized Penguin Bank as a pos sible volcanic vent. He reviewed what was known about the physiography of Molokai in a subsequent paper, and concluded that the main vent of East Molokai had probably been downfaulted beneath the sea.10 The presence of a large eroded caldera in East Molokai has been reported by Stearns.11 The fossil mollusca from the emerged reefs of East Molokai have been described by Oster gaard12 as late Pleistocene. Swartz13 noted briefly the results of G. R. MacCarthy's ground-water resistivity survey that was sub sequently summarized in 1042 in Department of the Interior Press Release 160579. Howell's 14 report gave a description of the plan and cost of transporting water from the streams of windward Molokai to the Hoolehua Plain for irrigation. In it was published a preliminary report on ground water in Wailau, Pelekunu, and Waikolu valleys by H. T. Stearns. Numerous unpublished reports relating to water· development exist. Among them are: M. M. O'Shaughnessay's report in 1899 to the American Sugar Co. on developing water power; W. Lindgren's report in 1900 to the American Sugar Co., essentially the same as his report published in 1903 by the Geological Survey; Frederick Ohrt's report in 1919 on water supply and power at Kalaupapa; H. A. R. Austin's report in 1919 to the Commissioner of Public Lands regarding a proposed domestic water supply for Halawa. his report in 1929 on water supply and power at Kalaupapa, and his reports in 1944 on projects to bring the water of the large

6 Powers, Sidney, Notes on Hawaiian Petrology: Amer. Jour. Sci., vol. 50, pp. 259- 260, 1920. 7 Bigelow, L. H., and Stewart, J. E., Report on the water supply and development of power at Kalaupapa, Molokai, by the Supt. of Public Works and the Chief Hydrogra pher & Engineer to the 1921 legislature: 55 pp., 1921. 8 Wentworth, C. K., The desert strip of West Molokai: Iowa Univ. Studies, new ser., no_ R!l, vol. 11, pp_ 41-n6. l 92!)_ 9 Hinds, N. E . .A., Maui and the Maui Group, Hawaii: Geogr. Soc. Phila., Bull., vol. 23, p. 150, 1925. 10 Hinds, N. E . .A., The relative ages of the Hawaiian landscapes: Univ. Calif. Pub., Dept. Geol. Sci. Dull., vol. 20, no. 6, pp. 170-182, 180-100, 1081. 11 Stearns, H. T., Large caldera on the island of Molokai, Hawaii (.Abst.) : Geol. Soc. .America Proc. for 1937, p. 116, 1938. 12 Ostergaard, J. M., Reports on fossil mollusca of Molokai and Maui: B. P. Bishop Museum 0cc. Papers, vol. 15, pp. 67-77, 1939. 13 Swartz, J. H., Geophysical investigations in the Hawaiian Islands: .American Geophy. Union Trans. of 1939, pp. 294-295, 1939. u Howell, Hugh, op. cit. INTRODUCTION 9 windward valleys, and of Waikolu Valley alone, to the Hoolehua Plain; J. Jorgensen's report in 1922 on a domestic water supply for homesteaders at Kalamaula and his report in 1923 on the possi bility of irrigating the Hoolehua homesteads with water from the streams on the windward coast of East Molokai; H. S. Palmer's report in 1928 on a proposed deep well in Palaau; M. H. Carson's report in 1931 to the Governor of Hawaii summarizing the reports available regarding the water resources of Molokai; H. T. Stearns' report in 1938 to the Chairman of the Board of Supervisors of Maui County regarding water supplies for Kaunakakai, and another in 1939 regarding Ahaino Spring and water supplies for Waialua; J. Matson's report in 1939 to Maui Oonnty es;timating the costs of the various possible water supplies for Kaunakakai; and C. K. Wentworth's report to the County of Maui in 1945, on exploration for and development of water supplies for Kaunakakai. 10' 157"00' 50'

KALAUPAPA PENINSULA

Miles

10' 157·00, 50' IHgure 2. Map of Molokai, showi11g the major geomorphic areas on the island. GEOMORPHOLOGY

Molokai consists of two major geomorphic areas: the East l\Iolo kai dome and the \Vest l\fololrni dune strip, windward cliff, northwest ridge, southwest ridge, and coastal plains. The northwest and southwest ridges are built over rift zones having those trends. ORIGINAL FORM OF EAST MoLOKAr.-East Molokai Mountain, prior to erosion, was a typical elongated basaltic shield-shaped dome, built over northwest- and east-trending rifts, with a steep slope on the north side where the lava flows plunged into deep water, and a gentle slope on the west side where the lava flows banked against the ,vest Molokai dome. The high cliff truncating the northern slope of Molokai is cut in weak basalts, and may be solely the result of marine erosion. Faults along the coast show downthrow to the south. If the windward cliff was due primarily to faulting, unless the faults along which the northern part of the mountain collapsed were considerably seaward of the present coast, one would expect the faults along the coast to show downthrow to the north, but no such faults have been found. Soundings along the northern side of Molokai are too few to delineate accurately the submarine topography. There are, however, enough of them to indicate the general nature of the submarine slope. The submarine portions of the sections in figure 3 arc based on projections of the few nearby soundings. The dashed lines in the sections indicate the original average slopes which would connect the lower portions of the profiles with the parts above sea level, assuming the absence of faulting. They are steeper than the slopes farther inland, as would be expected if the observed faults along the coast mark the northern edge of the caldera depression (page 30). None of the projected profiles are as steep as the actual southern slope of East Molokai above sea level. It is possible that the great northern sea cliff is a fault scarp battered back by erosion, as Dana, Lindgren, and others have hypothecated, but no faulting is necessary to explain the origin of the cliff, and it is equally or even more likely that no faulting was involved. The valleys of ·wailau and Pelekunu (pl. 5A) owe their great

11 w .•. 157"00' I "' I I I I

I I

Hooniki Island

----'=~-~3 miles I J, 1~7·00·

Feet 6COC-, PELEKUNU VALLEY Puu Alii Ptltpililau 422:z feet S~l"fO

Olokui Peak

4000

lU)OO ~000 ~~~ ----- ::~2000 ! --- 2000 1000 • • ·r0 ~: . ' ':: ."~~: ~~~~~:' ~~~~~ ;::::: WA.I LAU C VALLEY Mt7 feat lr\tltaitoo-.tuasu-eam ! ------____e=I~F Icr--____o_c EA JV _____

------, .,ooo

0000 ,0000 IOOOO 20000 Figure 3. Profiles across the northern slope of East: 1\folokni Volenno. The dashed lines show the projection of the submarine slope. Positions of the profiles are shown on the map. depth essentially to stream erosion, but their outlines were deter mined by an ancient caldera 41/2 miles long and 2 miles wide.1 5 The depth of this caldera at the close of volcanism is unknown, but it seems probable from the great amount of andesite extruded in the post-caldera stage that it may have been nearly :filled, resembling 15 Stearns, H. T., Large caldera on the island of Molokai, Hawaii (Abst.) : Geo!. Soc. of America Proc. for 1937, p. 116, 1938. 12 GEOLOGY 13 the summit area of Kohala Mountain, Hawaii.10 Erosion is rapid in these valleys now with a rainfall of about 100 inches annually. Prior to the great submergence of the Ha waiian archipelago the rainfall may have averaged about 500 inches annually in the summit area. Under such conditions, erosion would have been much faster than now. ORIGIN OF THE liOOLEHUA. PLAIN.-The Hoolehua Plain or isthmus of Molokai is composed of lava flows from the East Molokai Volcano banked against the older West Molokai Volcano. The lava beds dip 6° to 10° on the crest of East Molokai and only 1 ° to 3° on the Hoolehua Plain. Most of the plain is covered with 10 to 30 feet of lateritic soil. Overgrazing since white men introduced livestock and the cultivation of the land have accelerated erosion, and large flats of red soil washed from the plain are now forming along the south shore. Ancient Hawaiian :fishponds are being :filled with mud and mangrove swamps are developing. EMERGED A.ND SUBMERGED SHORE LINES.-The following shore lines, with the youngest at the top, have been determined to date in the Hawaiian Islands. Some are well preserved on Molokai.

Pleistocenel shore lines in the Hawaiian Islands

Approximate Type altitude Name Evidence on Molokai locality (feet) (island)

0 ...... Present shore line...... +5 Kapapa ,vave-cut bench at this level, and abandoned beach and dune deposits. Oahu +25 Waimanalo Terraces and marine deposits on East :Molokai. do. -60± Waipio Partly drowned dunes on West Molokai. do. +45 ...... Not identified on Molokai. +10 Laie Wave-cut platforms. do. +100 Kaena ,vave-c11t platforms and marine fossiliferous conglomerate. do. -300 Kahipa Not identified on Molokai. do. +250± Olowalu Fossiliferous marine conglomerate at this level, stripping of soil, nnrl wave- cut benches. Maui +325+ ...... Not identified on Molokai. Lanai +375± . .. " ...... Do. do . +u00 Manele Stripping of soil and wave-rounded boulders. do. +1200± Mahana Do. (only doubtfully identified on Molokai). do. -1200to Lualualei Deeply drowned valley mouths indicat- -1800 ing a large but unknown amount of submergence. Oahu

1 The shore lines older than the 250-foot level may be late Pliocene, although fossils from them have been classified as Pleistocene.

16 Stearns, H. T., and Macdonald, G. A., Geology and ground-water resources of the island ur Hawaii: Ilawaii Div. of Hydrography, Bull. 9, J.l- 181, 1946. 14 l\lOLOKAI

Gonthouyl• makPs tlu~ following statement, "At Molokai, an island a few miles northwest of Maui, Mr. B. Munn, teacher for the mission assured me that he had seen masses of coral apparently in their original position, embedded in calcareous rocks, one hundred and even one hundred and fifty feet above sea level." Coral frag ments are imbedded in limestone conglomerate 189 feet by level line above mean sea level in the gulch east of Pun Maniniholo.18 They are also present in the unnamed gulch a mile west of Kauna kakai Gulch to an altitude of 280 feet (barometer). Emerged reefs crop out east of the town of Kaunakakai at altitudes of 23 and 100 feet. Beach sand of the 5-foot sea covers a considerable area near Kaunakakai. Fossiliferous marine limestone veneers inter mittently many of the small gulches in this same area to levels up to 280 feet. The large gulches heading at the crest do not contain limestone probably because streams have removed it. The 560-foot shore line is traceable on the south slope of ""\Vest Molokai by the upward termination of black gypsiferous muds and a heavy cover of lag boulders. Spheroidally weathered boulders that lagged behind as the ocean swept a way the soil from between them characterize the slopes up to more than 900 feet and possibly to the level of the Mahana shore line inland of Kaunakakai (pl. 5B). On vVest Molokai lag gravel left behind by ·wind erosion forms armored deserts below the le,·el of the Manele 560-foot shoreline ( pl. 6B) . Penguin Bank, a,·eraging 180 feet below sea level just west of Molokai, is an extensive submarine platform indicative of a halt of the sea at this level probably during the Pleistocene. It is a com mon level throughout Pacific Islands but its position in the sequence of shore lines is unknown. Penguin' Bank may be capped by a drowned coral reef.

u Couthouy, Joseph P .. Remarks upon coral formationH in thP Pacific with sugges tiorn, as to the causes of their ahsence in the same parallels of latitude on the coast of South America: Boston Jour. of Natural Hist., vol. 4, p. 150, 1843-44. 18 Stf·arns. H. T., Pleistocene shore lines on the islands of Oahu and )Iaui, Hawaii: (}pol. Snf'. Am1>rica Rull., YOL 413, p. 1953, 1935.

Opposite page: Plate 4. The great cliff on the northern side of East Molokai. Kalaupapa Peninsula, in the foreground, is a younger basalt cone built against the cliff. The crater of the young cone (Kauhako Crater) is clearly visible. Dikes project as walls along the face of the cliff in the right forPground. Photo by U. S. Nav~r.

Plate GA. Pelekuun Yall<:.>.Y, East llololmi. The head of this huge valley is ex<.:an1H•d in the andent t:altkra complex of East ::\Iolokai Yokano. Tlrn floor is alluYiatPd owillg to rP<:ent dnnn1ing. Terraees near the• vallPy floor ,vere graded to former high stauds of the sea. Photo by l_:'. S. Army .Air Foree.

PlaU! GB. Sphl•roiLlal li011h1Prs 011 t hP ridgP we:c;t of Kmmakakai Gnkh. at H-10 frt>t altitrnh\ romH1Pcl h~· "·aYl' adion

L1nxG REEf'.-A living fringing reef extends along mnch of the south coast (pL 6A). It ranges from ;i to 3 miles wide. Red mud carried into the sea as a result of overgrazing in the last 150 years has buried much of the shoreward part of the reef. The shallow south shore was ideal for building fish ponds and the ancient Ha waiians built 53 ponds there, some as large as 500 acres, for raising mullet. Most of the ponds have been partly filled with mud in historic time.

GENERAL CHARACTER, AGE, AND WATER-BEARING PROPERTIES OF THE ROCKS The West Molokai Volcano built a shield-shaped dome of prim itive basalts from a northwest rift and a southwest rift. Apparently, no caldera indented the summit. The basalts were laid down in a highly fluid condition, as indicated by the thinness and high vesi cularity of most of the flows. Most of the vents were spatter cones but a few cinder cones were built near the close of activity. Vitric tuff deposits are scarce. After the dome ·was built about 1,400 feet above sea level, faulting dropped much of the northeast slope. ,veathering and stream erosion set to work to destroy the dome, but erosion was not very effective because the growing East Molo kai Volcano intercepted much of the moisture in the prevailing trade winds. Weathering continued, however, until deep soils formed over much of the surface. Then the dome was deeply submerged beneath sea level and later was partly emerged. These changes occurred so rapidly that the sea did little more than strip away soil along the leeward slope. ,vave action, however, cut a high cliff along tlw windward side. Numerous smaller emergences and submergences subsequently occurred that seem to be correlative with Pleistocene changes in sea level. For this reason extinction of the "\Vest Molokai dome is placed in the Pliocene. How long before that epoch the volcano started building from the ocean floor is unknown, and will probably forever remain so. The rocks of this volcano have been named the ,vest Molokai rnlcanic series. The East Molokai Volcano built a long narrow basaltic dome around a northwest rift, an east rift, and a central caldera. The last flows poured from vents on .1£ast .Molokai were andesites and tra chytes. The lavas of East Molokai Volcano overlapped the basalts of ,vest Molokai after the latter had decomposed to a soil 6 feet deep. However, the overlap is made by late flows of the East Molokai Vol cano and it is believed that the major parts of both volcanoes were 16 MOLOKAI lmilt concurrently, but that West Molokai became extinct first. The same high emerged shore lines are found on East Molokai as on West Molokai; hence, it is believed that the East Molokai Volcano also became extinct in Pliocene time. The rocks erupted by this volcano are called the East Molokai volcanic series. The Quaternary was chiefly a period of erosion and deposition. Relatively small quantities of limestone, calcareous dunes, and alluvium were deposited. During the late Pleistocene two eruptions occurred on the East Molokai dome, one of which formed the Kalau papa Peninsula and the other the islet, Mokuhooniki. All the volcanic rocks are very permeable except the dikes, which confine water at high altitudes on East Molokai, and a few thin tuft' beds which give rise to small perched springs. The West Molo kai volcanic series carries only brackish water because of the low rainfall on its outcrops. The stratigraphic rock units on Molokai and their water-bearing properties are summarized in the accompanying table.

TERTIARY VOLCANIC ROCKS

EAST MOLOKAI VOLCANIC SERIES The East Molokai volcanic series comprises all the volcanic rocks making up the East Molokai dome, except those in Kalaupapa Peninsula. I ts rocks crop out over an area 26 miles long by 8 miles wide. They are 4,970 feet thick above sea level and probably extend downward 12,000 feet more to the ocean floor. They have been subdivided into upper and lower members. A caldera complex forms part of the lower member. LOWER MEMBER LAVA. FLows.-The type locality of the lavas in the lower mem ber of the East Molokai volcanic series is the 1,800-foot cliff that separates Kalaupapa Peninsula from the rest of the island (p. 93). It is composed of thin-bedded vesicular pahoehoe and aa. The beds range from a few feet to 75 feet in thickness. Nonporphyritic and porphyritic olivine basalts dominate, but olivine-augite porphyries are common among the latest flows. Overlying the basalts, and separated from them by a layer of ashy soil 3 to 12 inches thick, are several flows of andesite belonging to the upper member of the series. The lower member is exposed wherever the upper member was not laid down, as between Wailau and Pelekunu Valleys, or where the upper member has been removed by erosion. All major gulches expose the lavas of the lower member. Stratigraphic rock units on the island of Molokai

Major geologic East Molokai Mountain West Molokai Mountain unit l------,------1------,--,-----,------

Rock General Water-bearing Rock General Water-bearing assemblage character properties assemblage character properties

Beach sand Rs Loose sand Highly perme- Beach sand 10± Rs Loose sand Permeable but chiefly basaltic able but carries chiefly carries brackish brackish water calcareous water in most places

Recent Highly perme- 10± Too Mixed bai:.altic Highly perme Dunes ~~~ii:entary I Dunes 1 · 50± Rd Loose able. They carry small ind calcareous able but carry calcareous sand brackish water to .:iand no water near the coast I show but no water inland Unconsoli- 20:;±:: Qa Silty gravel and Poorlv perme- Unconsoli- 10 ± Qa Silt. gravel. and Poorly perme Ooulder deposits able. ·They carry dated earthy poorly assorted able. They carry I i!~~~i~~rf~~t chiefly stream- fresh water in deposits bouldery small quantities rliff'erentiated laid. Also blocky small quantities nlluvJum of brackish on plate 1 talus at sea level in water from the eastern Molokai consolidated and brackish c>arthy water in central deposits) Molokai ------Local erosional unconformity------'------' Consolidated 200± Qa Consolidated They carry pota- Consolidated 100± Qa Friable deposits Poorly perroe- earthy and partly con- hie water in wet earthy I of reddish brown able. They carry deposits solidated depos- areas but usually deposits silt and bouldery small quantities its consisting of in small quant1- alluvium with of brackish older alluvium, ties. In dry area:,. minor amounts water near the ancient talus, they yield of talus coast landslide depos- brackish water its, and marine noncalcareous Pleistocene "!ediments sedimentary rocks Consolidated 5± Pm Patches of re~f Permeable but Consolidated 20.± lnurinc nmestone anct C'llrry only dunes Pd Consolidated Fairly permeable deposits breccias contain- brackish water and p3.:rtly but carry salt ing basaltic frag- in a few places eonsohdated water along the ments of lava. · cross~bedded coast and none Includes some calcareous dunes. inland patches of poorly! The compact consolidated

------a.Nat c:iroaional unoonform.ity----·------20--500 Ta Lava flows com~ The dense beds 1381+ Twb Basaltic lava Highly perme• posed chiefly of have low perme flows• composed able but carry dense and clink- ability but the of thin-bedded water too brack~ ery andesite and clinker beds are highly vesicular ish for humans trachyte usually very permeable. pahoehoe and aa nonporphyritic, They carry small They form the quantities of ~F~ite i:::r:ser f!::n;d water

(l) 25-300 Tac Cones consisting Highly perme- 25-110 Twc Cones consisting Highly perme- of cinder, able but carry f! bfa~fa~Jd~:~ !,b~fe~~\f:Jrfs~~ West Molokai tipatter, and thin salt water at the s lRy~r<;i of lava eoni;:t only § tt;t;;':it~n~~ M ~~~r~ifti;~ with vo1camc at vents lava fountains thf'se cones locally perch series small quantities of water

Tertiary East 50--200 Ta

Tb T~ci,·n fln'UT<;, c,nm- Highly pPMTIP.. posed of gener- able and freely ally thin-bedded yif'ld water to moderately to wells and tun hig-hly vesicular nels. They carry ~asaltic pahoehoe only brackish and aa ,vater along the coast of central 1Iolokai

20-150 Tbc f'onPR eorrnisting Highly pPrme- of ('Ompact able hut carry no fPd cinrlns and water. ThP cor thin :;.eoriacf'oouR: rPlative tuft'" bedR flo,vs at Tf.'nts TH:>rC'h wnter in wet areas

Dikp,;; ('OffiDORP(l f'ontlnP watPr as ~ 1h-15 Red lines <'hiefly of tiPnRe mn('h a,; 2.000 ('rOl-'l8-ioint€'rl fPPt ahovP ,;ea e hasalt hnt a f€'w lPvPl in the dike are vesicular and <'omnle~es. ).fo,;it a platy. A few nnPnnial water twlOngJng- to rne l": ~upJflle11 ny upper member rhkP ,::trnctnrPs ~ are not differen- .s tiated on plate l

1000± Tc Caldera complex Xot vPry pPrm{\~ of vent breecia8. nhlP 118 a whole Ia·rn flows, plugR. but yields per~ !':tocks. talus, and ennial springs pyroclastic rocks nt high levels that accumulated in and under the summit caldera. The vesicleR are ('ommonly filled ,,ith pneumato- litic secondary minerals GEOLOGY 17

The basalts weather to dark-gray, red, red-violet, and brown and stand in sharp contrast to the upper member which weathers to light-gray and white. Dark-red and reddish brown soils character ize the decomposed surface of the lower member. The lavas are decomposed for a depth of 50 feet or more in flat areas where the soil has not been eroded away. The beds accumulated rapidly as Rhown hy the absence of interbedded residual soils and alluvial deposits. The beds dip 3° to 15° away from the axis of the dome, except on the north coast between Waikolu and Wailau Valleys, where they dip southward 8° to 25° as a result of faulting. The basalts are highly permeable and are the principal aquifer of Molokai. They carry brackish water in the western end and potable water in the middle and eastern end of EaRt Molokai. CONES AND Vl'.l'1uc TUFF DEPOSITs.-Five cinder and spatter cones that erupted basalts lie on the western slope of East Molokai. Many others must be buried by the upper member. Several cones inter bedded with lavas of the lower member are exposed in Waikolu and Kaunakakai Canyons. Thin lenses of weakly consolidated vitric tuff are common in the gulch walls in the south central and eastern part of East Molo kai. Apparently the prevailing northeast trade winds carried Pele's hair and pumice from the lava fountains and from adjacent cones in the caldera to these areas. The beds are too discontinuous to shov!' on plate 1 and they rarely exceed 3 feet in thickness. Three prominent thin vitric tuff beds crop out in the east wall of Pelekunu Valley where they perch high-level springs yielding about 1,000,000 gallons of water per day. Elsewhere they rarely carry perennial water. lNTRUSIVEs.-The intrusives of the lower member of the East Molokai volcanic series comprise a dozen or more stocks and plugs, hundreds of dikes, and a few short sills. All the stocks lie in the caldera complex. The texture of the stocks ranges from coarse grained basalt through porphyries to coarse gabbros ( See Petrogra phy). The stocks occur chiefly in Wailau Valley. None of them exceed half a mile in diameter. A few lenses of dense rock, probably crater-fills, are exposed in the walls of Waikolu Valley and some of the other deep gulches. Two great systems of dikes spread from the ancient caldera in Pelekunu and Wailau Valleys, one to the east and the other to the northwest. A few divergent dikes also crop out. The dikes range from a few inches to 15 feet in width and average about 2 feet. Multiple dikes are common. Some of the wide dikes are andesite 18 l\IOLOKAI .iud fed the flows in the upper mem~er of the East Mol?kai volcanie · Tl y lia,·e not been differentiated from basalt dikes on plate series. 1e < l. :Many are cross-jointed but some are platy and vesicular. Most are bordered by glassy selvages 1/s to ~ inch wide. The dikes range from fine-grained basalts to porphyries containing augite, olivine, and feldspar phenocrysts. A few are andesites. Only a few in 1Vailau and Pelekunu Valleys are plotted on plate 1 because they are too close together to be shown. The strikes of 265 dikes were recorded in Wailau Valley and many other dikes were noted for vthich no measurement was made. Thirty-eight dikes are exposed in ,vaikolu Valley and several hundred in Pelekunu Valley. An unusual dike is exposed in the east side of Pelekunu Bay. It trends due north and is 2 feet wide. It has joints 3 to 4 inches apart parallel to the walls with the middle part of the dike made up

:Figure 4. Diagram of a dike on the eastern shore of Pelekunu Bay, showing arched bands of yesicles. GEOLOGY 19 of arcuate lines of vesides a few inches apart. "\Veathering along the vesicles has b1·ought the intervening oense rock into relief, giv ing the dike the appearance of a series of curved parallel ribs (fig. 4). The dike swarms and dike complexes are the great water-bearf'rs of East Molokai Mountain. The water is stored in the intervening pPrmPah]e basalts. Dikes crop out at the head of every major valley and supply nearly all perennial streams, and provide a total low flow of about 9 million gallons daily. The water issues from dike swarms between 1,200 and 1,800 feet above sea level in Wailau and Peleknnn Valleys, between 300 and 900 feet in vVaiohookalo Valley, and be tween 250 and 1,400 feet in \Yaikolu Valley. The proposed East Molokai project would depend for its low-water flow from tunnels penetrating the dike complexes. The plugs and other large intrusivP hodies of rock are so dense and the joints so tight that they are poor water-bearers. CALDERA COl\IPLEx.-The caldera complex of East :Molokai Vol cano lies in Pelekunu and Wailau Valleys, and forms a part of the lower member of the East Molokai volcanic series. The larger mass is 4% milPR long and 11/2 miles wide. A smaller mass about 1 mile in diameter borders the southeast side of Haupu Bay (pl. 1). The complex is composed of stocks, plugs, crater fills, ponded la,-as, and talus and fault breccias cut by dike swarms. The rocks accumulated in and under a caldera about 41/2 miles long and 2 miles wide. Much of the area of these rocks shown on plate 1 is covered with older alluvium. The complex crops out chiefly in stream beds where the older alluvium has been cut away. Detailed traverses were made on foot up each tributary of Wailau and Pelekunu streams, but the results could not be plotted on the topographic base map (pl. 1) because the stream pattern shown on the map is seriously in error. For this reason outcrops had to be generalized to fit the base. The rocks making up the complex are readily distinguished, in the field, from those formed outside the caldera by the presence of calcite, quartz and secondary minerals deposited by h;vdrothermal action in preexisting cavities, by a great variety of breccias, ma:::l sive lava flows, stocks of gabbro and coarse textured basalt: and by fewer dikes than in the lavas adjacent to the complex. Some of the dikes must have intruded masses of hot rock, as they lack typical glassy selvages and in places merge with the rock they intruded. The coarse-grained gabbro in the southwesternmost tributary of \Vailau Valley is unusual in Hawaii. Numerous types of breccias can be distinguished in the caldera complex. The commonest is talus breccia, composed usually of 20 l\IOLOKAI . . ome of which are 6 to 10 feet across. Talus exotic fragments, s . f the complex nnd locally bre-ccia is abundant along the marg:ms 0 . . rl pit craters have perforated the mass. w1tlun the comp1 ex " iere . . • b · contain more vesicular rock than the pit The margma1 reccias _ · b ause the pit craters usually had walls of massive crater breccias, ec . hat yielded dense fragments. All the breccias are ponded 1ava t . . d . t h. h . th usuallv well cemented with s1hca an iron, excep ig 1n e sectio~ near the former :floor of the caldera. There they are poorly cemented. These poorly cemented breccias would be distinguished with difficulty from talus breccia in the older alluvium if it were not for dikes cutting them. Some lenses of massive lava carry numerous vesicular fragments near their bottom. The fragments are usually rounded by resol.1) tion but some are angular. The fragments are similar in composi tion to the matrix. These breccias are believed to have been formed by· vesicular crusts sinking in a lava lake, a feature commonly observed at Kilauea Volcano, Hawaii, during its lake phase. Small patches of talus breccia were noted among the crusts in a few places. These patches are former slides from crater walls into lava lakes. Where slight collapse of a solidified basaltic mass has occurred the breccias consist of fragments of one rock type only cemented in a matrix of the same rock. One breccia of this type was noted in which the matrix was apparently fluid at the time of the collapse. Breccias of this type probably result from the subsidence of a partly solidified lava lake. Fault breccias and crack fills are identified by their longitudinal outcrops. The former usually show well-developed slickensides bordered by a few inches of gouge. The friction breccias along faults usually are crushed into small, sharp fragments. The frag ments of some shattered blocks ha.ve hefln only Rlightly ilispfaced, 8 feature rarely found in other types of breccias. Some stocks carry fragments of fine-grained basalt in a coarse grained matrix and are typical intrusive l,1·ecdas. One intrusive, in, Wailau Valley, is composed of angular fragments, reaching a foot across, of coarse-textured dense basalt in a matrix of' feldspar and augite crystals averaging a third of an inch across. Some gabbros carry partly resorbed blocks of gabbro. Some of the intrusive breccias in this valley may be the result of the collapse of the solidified roofs of plugs. In a few places talus breccia underlying solidified lava lakes has been fused. The welding usually extends downward only a few feet. The most difficult breccias to interpret are those formed by former Plate (U... Southern slope of East 1IolokaL showing tlw fringing eoral reel' nn!l the nlln\'ial flats :dong the eonst. Kanmlo \Yhnrf is in the for(?gronn

Plate GB. Armored desert ou the southern slopl· of \\'pst }Iolokni. The lag gravel was left behind l)y wincl erosion. but tlH~ soil was largelr strippe< l a wa.\· and the cobbles were romH.lPd by ,vaYe adion clnriug the high stanet of the seu ,vhich left the }lanele ( GGO-foot l shoreliue. Photo by H. 'r. Stearns. Plait~ 7A.. Hcw.l of Kaumlo Gukll. Ea:,,t Mololrnl, showing the eiwracteristie t bin hPdd andesite Nlp. The l1cight of the amphi thPater head-wall is nhout 1.GOO feet. Photo by G. A. ::\:Iaedmrnld.

Plate 7B. The ::-ea cliff on the northern coast of ,Yest ::\lolokai, looking (•ast ,vard to ::\lokio Point from 11Par Kat•o eonr•. The cliff. ,vhkh is about 500 feN high, exposes rnni1y dikes ill the 11orrhw<•st rift zone of ,YPst ::\iolokai. Kaa cone lies on the sk~·line. Photo llr G. A. :Macdonald. GEOLOGY 21

"floating" islands that crashed to the bottom of a lava lake during rapid subsidence. They are clinkery and vesicular masses of very irregular form, commonly of large size, and chiefly of one rock type in a matrix of cemented reddish rock flour. Xear the amphitheater head of Wailau Valley, a few of the tributaries have cut to the contact of the complex with the extra caldera lavas. The streams cas'cade alternately on ancient talus breccia, deposited along the caldera wall, and on thin-bedded pre caldera lavas cut by dike swarms. The lack of faulting gouge and other evidence of movement at the contact indicate that this par ticular talus breccia accumulated at the foot of a cliff. The south edge of the caldera complex in the head of Pulena tributary of Wailau Stream is bounded by a well exposed fault trace. An excellent exposure of the ancient caldera wall lies in the west fork of Pilipililan Stream at an altitude of about 1,200 feet. The wall dips 60° to 80° to the east. In the wall, typical massive caldera filling lavas dipping slightly to the east rest unconformably against thin-bedded pahoehoe. Breccia composed only of the rocks in the wall underlies the massive basalts. Single flow units in the ponded lavas in the caldera complex are commonly 50 feet thick and a few are 75 to 100 feet thick. '!'he extra caldera basalt flows rarely have flow units more than 15 feet_ thick. The Haupu Bay mass is interpreted as a pit probably not con nected to the caldera, similar to the relation of Lua Hou to Mokua weoweo Caldera on Mauna Loa Volcano, Hawaii. The rocks are chiefly breccia capped by massive crater-filling lavas. The contact of the breccia and the crater wall is well exposed in the sea cliff on the eastern side of the bay. There 100 feet of breccia is exposed striking N. 10° E. and dipping 28° NE. under massive flows striking N. 70° W. and dipping 15° S. The crater wall strikes N. 15° W. and dips 60° NW. The inland boundary of the crater as shown on plate 1 is hypothetical, as the contact could not be traced in the field. There is some evidence suggesting that this crater was buried by lavas from the main caldera long before the completion of ihe East Molokai dome. The <'a.ldera complex yields little water, even though it receives heavy rainfall. This small yield is due to the low permeability of the major part of the rocks and to the discontinuity of structures. However, lhere are many small springs in the area, the aggregate of which comprises a goodly share of the flow of Pelekunu and ,vailau streams. Many of the springs discharge from the alluvium overlying the caldera complex although the water is largely derived from the underlying complex. Many of the tributaries were traced 22 )IOLOKAI back to the canvon heads where the springs ·were found issuing from the dike swar~s in the extra-caldera basalts. Thus the proposed tunnels to develop water for the Molokai project (p. 82) ·will prob ably obtain their largest yields after they leave the caldera complex and penetrate the extra-caldera basalts.

UPPER MEMBER

LAVA FLows.-The upper member of the East Molokai volcanic series consists chiefly of oligoclase andesite with lesser quantities of andesine andesite and trachyte. These rocks once formed a veneer over most of East Molokai. The upper member averages about 500 feet in thickness along the crest where it is composed of numerous flows, antl thins to t>O feet or less on the lower slopes. The thinning is largely due to the flows having been so viscous that few reached the periphery of the dome. In many places erosion has removed om~ or two flows. The flows range from 20 to 100 feet thick and form conspicuous rimrocks to the gulch walls (pls. 7A, 14A). All the lavas are aa and many carry heavy clinker beds. The dense parts of the flows are columnar jointed and usually platy, especially near their base. The lavas are generally non-porphyritic but a few carry feldspar pheno crysts (See Petrography). The upper member serves as a protective armor over the easily eroded lower member; hence, most streams have falls or cascades where they cut through into the weaker basalts. -where these thick lava flows spread out famvise as they moved tluwn the slopes they caused streams to diverge from their normal course radial to the dome and follow the edge of the lava flow diagonally across the slope. Thus some streams, such as Kamalo, have received more than their share of the drainage and have cut abnormally deep amphitheater-headed canyons. The heavy :rndesite armor is respon sible for swamps such as the one east of ,vailau Valley remaining undrained while deep gorges were being cut in the weak basalts near by. No erosional unconformities were found between the andesite fl°'vs, but interbedded ashy soil beds are fairly common. The upper and lower members are usually separated by a few inches to a foot of red soil, indicating that only a short time elapsed between the laying down of tlw basalts and the andesites. The type locality of the upper member is along the trail down the windward cliff to the Leper Settlement (p. 93). There three or more flows of andesite, aggregating 200 feet in thickness, overlie the basalt with ~ to 1 foot of intervening soil. GEOLOGY 23

The dense beds of the upper member have low pPrmPabilit~·, but the clinker beds are very permeable. Most of the perched ,vater in the eastern part of the island of Molokai issues from the top of outCl'ops of interbedded ashy soils in the upper member. CONES AND BULBOUS DO)IES.-Eruptions of andesite and trachyte were usually accompanied by lava fountains that built bulky cinder cones. of which 25 are shown on plate 1. Some of the hills in the swamp east of vVailau are probably cinder cones also but no ex posm·es are available. Some of the lavas were extruded in so viscous a state that they made bulbous domes. These usually formed after the gas had been discharged during the la,·a fountain stage. Ten sucll domes are mapped on plate 1. Some of tile peaks along the crest may be the ma1·gins of bulbous domes also, the northern part having; been cut away by ,vailau and Pelekunu streams. Puu Kaeo and Hanalilolilo hiU, near the head of ,vaikolu Valley, are bulbous domes. The nearby Kaulahuki hill is a large andesite cinder cone, partly eroded to expose a bulbous dome and plug in the crater. A bulbous dome is shown at the head of the andesite flow forming the eastern rim of Kamalo Gulch, although positive evidence of the extrusion was not found. The cones and domes are not water beare1·s. Dikes belonging to the upper member were not mapped separately on plate 1. Most of them are wider than the basalt dikes.

EROSIOKAL UXCONFORMITY The unconformity between the East and "~est Molokai volcanic series is ,vell exposed in the east bank of ,vaiahewahewa Gulch at an altitude of 250 feet, 2 miles from the mouth. The section con sists of 30 feet of lateritic soil resting on a flow of basaltic pahoehoe, containing; phenocrysts of augite, olivine, and feldspar, from the East )Iolokai Volcano. Beneath this.there is 3 feet of blocky baked laterite grading do,vmvard into 6 feet of spheroidally weathered high}~, vesicular nonporphyritic basaltic pahoehoe from the ,vest Molokai Volcano. The contact strikes N. 50° ,v. and dips 10° NE. The deep soil between the two lavas indicates that this slope of West }lolokai had long been extinct when the lava flows from East Molokai finally buried its eastern slope. ,vaiahewahewa Stream has been turned from its normal eastward course to a southerly eonn;:e by the lavas from East Molokai.

WEST MOLOKAI VOLCANIC SERIES DISTRIBUTION.-The West Molokai volcanic series is named from ,vest l\:Iolokai Mountain, which is composed of volcanic rocks erupted 24 l\IOLOKAI

from a shield-shaped dome (pl. 6A) rising 1,381 feet above sea lernl locally known as Mauna Loa. However, the name Mauna Loa is avoided herein because of the confusion which might arise with the well-known Mauna Loa on the island of Hawaii. The rocks crop out over an area 12 miles long and 10 miles wide (p. 1). The lavas have weathered into such deep soils that over large areas little original structure can be discerned. CHARACTER AND STRUCTURE.-The lavas of the West Molokai volcanic series are all basaltic and mostly exceptionally thin-bedded and non-porphyritic. Olivine basalts, basalts, and primitive-t;rpe picrite-basalts occur (page 105). The flow units aYerage about 2 feet in thickness. The beds dip from 2° to 10° away from the southwest and northwest rifts and the dips are steepest along the south slope. Many of the beds converge toward the summit where the two rift zones intersect. Both aa and pahoehoe exist. The beds in the fault block area on the eastern side, especially 112 mile southeast of the summit, are considerably bleached and mineralized by hydrothermal action, presumably by gases that rose along the faults and dikes. Fragments of chalcedony and calcite several inches across are common in the stream beds draining this area. Fragments of secondary spongy brown iron ore as much as 6 inches across lie in this area also. Elsewhere the vesicles are not filled, ex cept locally with a soft cream-colored deposit probably allied to montmorillonite deposited by percolating ground water. A few of the latest flows, notably the one from Waiele c.:une, are underlain with 112 to 4 feet of red ashy soil. These are shown in figure 18. A bed of breccia carrying blocks up to 2 feet across lies in the south wall of Waiahewahewa Gulch half a mile south of the summit. ThP- lavas in West Molokai carry bracki'sh water suitable for stock along parts of the coast but none that is potable for humans. The test well drilled by Libby, McNeill, & Libby 3 miles northwest of the sulllmit has demonstrated that these lavas do not carry potable water even 2 miles from shore, due to the low recharge and the large amount of salt carried to the water table from salt spray blown inland by the wind. This well is slightly thermal and alkaline, probably indicating rising volcanic gases admixed with ground water. CONES AND VITRIC TUI<'F DEPOSITs.-Seventeen spatter and cinder cones were mapped on West Molokai. Many other small hills are probably cones but weathering is so deep that no rocks are exposed. Kanewai, Puu o Kaiaka, and Waiele are the largest cones, each covering about half a square mile. Kaiaka fa 110 feet high and is GEOLOGY 25

chiefly composed of cinders. Kaeo cone and a few othm•s eonfain dense beds of basalt that have been extensively quarried by the ancient Hawaiians for making stone adzes. The northern end of Kaa cone is a plug of dense basalt, exposed by erosion. Thin vitric tuff deposits lie interstratified with the lavas, especially in the wind ward cliff near Ilio Point, but are too small to show on plate 1. The lavas apparently accumulated rapidly, typi'?3.l of the early phase of Hawaiian volcanoes. DIKES.-Thirty-two dikes averaging about 2 feet thick are ex posed in the sea cliff cutting the northwest rift (pl. 7B). They all strike northwest (pl. 1). About 20 dikes and numerous dikelets. striking chiefly southwest, are exposed in vVaiahewahewa Gulch near the summit. The gulch has just begun to cut into the heart of the West Molokai Volcano. Many other dikes are probably covered with alluvium in this area. The widest dike is 10 feet across, but mostly they are 1h to 2 feet wide. Two basalt dikes crop out in the southeast corner of ,vest Molokai at the coast. Both strike N. 70° W. and range from 6 to 10 feet in width. The western one connects with a lava flow 10 feet thick. The dikes probably confine water appreciably above sea level in the rift zones a mile or two from the coast, but because of the low rainfall and salt carried downward from spray, it is not potable.

QUATERNARY VOLCANIC ROCKS KALAUPAPA BASALT The Kalaupapa basalt is named from the leper settlement which is built on this lava. The basalt forms a peninsula 2% miles long and 2% miles wide projecting from the base of the great windward cliff of .1£ast Molokai Mountain (pls. 4, 8A). The lava is a porphyritic olivine basalt pahoehoe (See Petrography) that issued from a flat lava cone 405 feet high indented with a crater a quarter of a mile wide and more than 450 feet deep. A brackish · pond lies in the crater. Two distinct rock benches in the crater indicate that the lava lake halted twice during the recession of the magma column. Most of the lava discharged northward through a large lava tube that is now collapsed. Several other tubes are exposed at the sea where they have been eroded to form natural bridges, blow holes, and other scenic forms. Most of th~ cone lies under the sea. The lava flows forming the cones are essentially contemporaneous with each other and are only slightly decomposed. Long tumuli are common and thin flow units are characteristic. .. 26 }UOLOKAI

·t f ·al ~and shells, and boulders reach a height I,oose. (1 epos1 s o cu1 " , . . . ·•- f t . l a tlie northeast coast of the penmsula. They md1cate o f ·•·> ee a on 0 • • the 5-foot and possibly the 25-foot shore Imes of late Pleistocene tim('. Conglomerate overlying the ,.b~s~lt forms a terrace 100 feet above sea level near the mouth of,, aileia Stream. It is the remnant of an ancient alluvial fan graded to a stand of the sea at least 25 feet higher than the present. The Kalaupapa basalt is assigned oll this evidence to the late Pleistocene. The Kalanpapa basalt is highly permeable bnt carries only brack ish water.

TUFF OF l\lOKUHOOXIKI COXE The remains of a large basaltic tuff cone lie 1 mile off the eastern end of ::\Iolokai. The cone has been cut in Lwo by the waves. The northern part is called )fokuhooniki and the southern part Kanaha. Moknhooniki is 203 feet high. The cone is typical of those formed by phreatomagmatic explosions and resembles Manan,a Island otf Oahn. Lithic fragments and blocks of coralliferous limestone abound in a palagonitic matrix. During thP- closing phase of the eruption spatter was thrown out and lava flows cascaded down the leeward slope of the cone. Several thin dikes cut these islands and a large vertical cave lies along one of them. One dike has controlled ,vave erosion in such a way that the bench on the windward side is 5 to 8 feet above sea level, whereas the one-on the leeward side is 1 to 3 feet above mean sea level.1 9 It is probable that these benches have been dressed dowu from those left by the 5-foot sea. The eruption is believed to have occurred in late Pleistocene time. The tuff of l\fokuhooniki cone does not carry fresh water.

SEDIMENTARY ROCKS

CAUAl{J<;UL:S .iUAIUNE DEPOSITS.-The older calcareous mari.ne sedi. ments a1·e breccias and poorly developed fringing reefs usually 1 to 8 feet thick. They lie chiefly in two ledges east of Kaunakakai (pl. 1) at about 25 and 100 feet above sea level (pl. 8B). Fossil nullipores and corals are abundant as well as foraminifera and molluscs. The latter have been identified as of Pleistocene age.20 The marine deposits above 120 feet lie chiefly as thin intermittent veneers in the gully bottoms. They reach a height of about 280 feet above

1 9 Stearns. H. T., Shore benches on the island of Oahu, Hawaii: Geol. Soc. America Bull., vol. 46, p. 1474 and pl. 132, 1935. 20 Ostergaard, J. M., Reports on fossil mollusca of Molokai and Maui: B. P. Bishop Mu:seum -Oee. Papers, vol. HI, pp. 67·77. 1939. .. Plate 8.\. Kalaupapa l't-·uiw;ula. al the l>HM' 11f' the uortlHTll cliff ol' En'4t }Iolokai. from the month of \\'a ikoln \'a Ik.L ThP IH·lli 11:,;nla b a :,;mall lia:,;alt ('OIH' bnilt against the dilT. The tL'ITH<·P in the rniddlt> 1li:,;ra1l<'L' b a gm Yd (lppo:,;it gr:Hletl to the \\'airnmmlo (:!3-foot) :,;taml ot' the' sPa. l'hoto 11)· II. T. Stearlls.

l'latc! SB. HL!ef li1upstonc of tlw \\'airna11alo 1:!3-foot l starnl ol' tlw :,;pa, rc:,:t iug on partly decompose(! gran~l. ill a roadeut 1.--1: milp:,; ea:,;t ot' Kauuakakai. l'lloto lJ,y G. A. )lacduualtl. l'lat<• !JA. Lithified li<•ach smHlst01w 1wnr Hakna. on ihe soulhern shore of "\Yl'Sl ::\lo]olrni. I'110W ]l)' C. K. "\Yc•JJ[ \\OrllJ.

l'la tP !lB. Gn1 Yel u•rra<·e n t the lllon th of "\Y nilPia Ya lJp~-, rPstiug on 11H· Kalanpava basalt. TllP tPrrace was grndv<1 to ihe "\Yaimnwdo 1+2:-i-foot l stnrn1 of the SPa. /\ SP<·(111d tl'rr;we bd1iun the Hoolehua Plain. A nearby continuous narrow plain of alluvium borders the southern edge of East Molokai (pl. 6.A.). :N" ear Panahahe Fishpond a thin capping of basaltic gravel contains shells of marine molluscs up to about 25 feet above sea level. The alluvial deposits are usually weakly consolidated and in wet areas are partly or completely dPcomposed. Much of the allu vium is composed of ochre to red-brown conglomerates, usually coarse and poorly sorted. Boulders 10 to 20 feet across are common i.n it i.n Wailau and Pelekunu Valleys. Some deposits resemble mud flows because they were laid down by torrential streams. They gradt~ into coarse blocky talus near canyon ,valls. The older alluvium is several hundred feet thick in most of the windward valleys and at the mouths of the large gulches extends several hundred feet or more belo,v sea level. In some places in ,vailau and Peleknnn Valleys, the alluvium is sufficiently cemented to form cascades and water falls but in other places it is easily cut by a shovel. On the Hoolehua Plain it is chiefly silty and friable.

21 Stearns, H. T. and Vaks,ik, K. N., Geology and ground-water resources of Oahu, Ha,,n,ii: Hawaii Div. of Hyclrography Bull. 1. PP. 41-42, 1935. 28 MOLOKAI

The older alluvium in the major valleys forms two or more ter races, which indicates that it was laid down at different times. During high stands of the sea in Pleistocene time the valley floors were aggraded (pl. 9B) and during low stands the streams cut deeply into the alluvium. In places major streams have not yet cut down to their former bedrock floors even far inland. Most of the alluvium has low permeability but in Wailau and Pelekunu Valleys many small springs and seeps discharge from its base. One such spring in the southwestern part of vVailau Valley yields about 100 gallons of water per minute. It comes from the base of a boulder deposit filling a narrow gorge cut in dense volcanic breccia. It apparently rises, however, from a dike swarm not far from where the spring issues, and represents an exhumed spring buried by the alluvium during a period of aggradation. Valuable supplies of domestic water have been developed by dug wells in the older alluvium along the south shore. CONSOLIDATED DUNEs.-Stretching 2 miles southwestward from Moomomi Beach on West Molokai are consolidated dunes 5 to 23 feet high (pl. lOB). They migrated over a cliff 600 feet high before they became cemented. Another large outcrop lies at Ilio Point and smaller outcrops lie along the coast east of Moomomi Beach (pl. 1). The sand is chiefly comminuted coral, shells, and foraminifera with small amounts of basaltic sand. The dunes show several degrees of consolidation. The oldest sand is the hardest and is cemented into a firm rock called eolianite. Near Ilio Po~t this rock extends below sea level (pl. lOA). It is benched by the 5- and 25-foot stands of the sea. Fossil shells of land ·snails are abundant. These older dunes, in common with those elsewhere in the Hawaiian Islands, formed during the late Pleistocene when the sea level was about 60 feet lower than at present. Their relation to the sea cliff on West Molokai shows that most of the marine erosion which formed the cliff occurred before the minus-GO-foot stand of the sea. The dunes are permeable. They carry salt water along the coast and no water inland where they rise above the water table. UNCONSOLIDATED DUNES.-Extending 51/2 miles southwest from Moomomi Beach is a strip of unconsolidated dunes half a mile wide composed of cream-colored "coral" sand (pl. 1). Much of it has been blown from the older weakly consolidated Pleistocene dunes. The dunes reach a height of about 60 feet near Moomomi Beach. A few dunes, too small to show on plate 1, lie at Papohaku Beach. Most of the sand seems to have been derived from the former mar ginal ocean floor when it was bared during the Waipio low stand GEOLOGY 29 of the sea. The dunes carry brackish water near the coast but no water inland. BEACH DEPOSITs.-Cream-colored deposits of loose sand composed of comminuted corals, nullipores, molluscs, foraminifera, and other marine organisms form narrow beaches along much of the shore of "\Vest Molokai. The largest deposits are at Papohaku and Moomomi beaches. A few lie near Kaunakakai, and contain much comminuted basalt. Much of the leeward shore of West Molokai has red silt beaches formed by the waves reworking the torrential deposits brought by streams from the uplands. A black sand beach formR annually at the mouth of Wailau Valley during the summer months but is carried away by winter storms. Black sand beaches also occur near Waialua and between Kawela and Kaunakakai. Cobble beaches characterize the reentrants along the windward coast and a few stretches uf eastern leeward coast. The beach deposits carry potable water in some of the stretches in the wet eastern end, but only brackish water on western and central Molokai. UNCONSOLIDATED EARTHY DEPOSiTs.-The loose earthy deposits are chiefly poorly sorted, puurly rounded stream-laid brown silt, sand, gravel, and boulders lying in Recent stream channels. Many narrow bands along streams are too small to show on plate 1. They range from a few inches to 50 feet in thickness and form fans at the mouths of the gulches along the leeward coast. Extensive aprons of blocky landslide deposits lie betwePn Ha.lawa and Wailau valleys along the windward coast and at the foot of the cliff on Kalaupapa Peninsula.

GEOLOGIC STRUCTURE EAST MoLOKAI.-The E.ast Molokai Mountain is an asymmetrical shield-shaped dome elongated eastward and westward and built about an ancient caldera in \Vailau and Pelekun11 valley8 (pl. 1). The east-west elongation of the dome is due to the presence of north west and east rift zones, from which lavas have been extruded. The beds have centrifugal dips of 2° to 15° away frurn the volcanic center except along the lower part of the great northern sea cliff, where the beds dip 8° to 25° S. The apex of the dome is missing due to collapse and erosion. No folding was seen. The caldera complex is bounded by normal faults, but the downthrown segment is not recognizable, possibly because it sank largely as thin peripheral slices which shattered to form breccia. The absence of explosion debris interbedded with the extra-caldera lavas is positive 30 l\IOLOKAI

evidence that the caldera formed by subsidence rather than by explosions. Faults are numerous near the mouth of Pelekunu Valley and in the cliffs bounding Haupu Bay. The main fault on the east shore of Pelekunu Bay strikes east-west and dips 57° S. The slickensides along the fault trace are well exposed as the gouge is more resistant to erosion than the adjacent rock so that the hanging wall has become an overhanging ledge 8 feet high. The gouge is 3 to 6 inches thick and fa bordered by breccia with blocks reaching 2 feet across, many of which are slaggy pahoehoe. The pahoehoe on the south side has drag dips of 35° S. adjacent to the fault plane, but 10 feet away it dips only 18° S. Tiu~

22 Stearns, H. T. and Clarie ,v. 0., Geology and water resources of the Kau District, Hawaii: U. S. Geol. Survey Water-Supply Paper 616, pl. 1, 1930. GEOLOGY 31 thin-bedded lavas can be seen on Molokai, and for this reason it seems unlikely that the southward dipping lavas came from a vol cano now beneath the sea north of the present coast. The swarm of faults dipping southward parallel to the great sea cliff of Molokai suggests the possibility that this cliff is an obsequent fault-line scarp and wave erosion has been halted by the heavy ponded lavas in the downthrown blocks. A similar condition ,vas noted in the great cliff of Kauai.23 "'\VEST 1\foLOKAI.-The ,vest Molokai Mountain is made up of two broad fairly flat constructional arches, one extending southwest ward and the other northwestward from the summit. These arches resulted from building along rift zones haYing those trends. The northeastern side of the dome is terminated in a set of echelon fault scarps, 100 to 500 feet high, facing northeast,vard (pl. 12A). The downthrown part of the dome lies under Hoolelrna Plain and is buried by lavas from the East Molokai Volcano. The locations of the faults are shown on plate 1. The actual fault traces are not well exposed, but the fault-scarps are only slightly modified by weathering and erosion:

GEOLOGIC HISTORY

The amount of submergence of Molokai is unknown, but it must have been large as indicated by the deep drowning of the mouths of the large canyons. It is probable that the submergence is of the order of 1,200 feet, in common with the other islands of the group.

TERTIARY TIME 1. Building of a shield- or dome-shaped island of thin-bedded primitive basalts at the site of West Molokai Mountain. 2. Growth of the East Molokai Volcano above sea level with the eruption of the thin-bedded basalts in the lower member of the East Molokai volcanic series ( fig. 5, stage 1) . 3. Extinction of the \Vest Molokai Volcano and downfaulting of its northeastern side. ,veathering develops a soil cover and streams erode its slopes (fig. 5, stage 2). 4. Continued eruption of the East Molokai Volcano, accompanied by collapse of the summit to form a caldera 41h miles long and 2 miles wide. Faulting may have dropped part of the north side of the cone during this or later stages. Lavas from East

23 Stearns, H. T., Geology of the Hawaiian Islands: Hawaii Div. of Hydrography Bull. 8, p. 89, 1946. 157°00' 50' 40' 20' ICY

EAST MOLOKAI VOLCANO 21°10'-+------'

p C I .F I C 0 C E A N I

21 10'

20' 10' 157'00' 50' 40' Figure 5. Drawings illustrating six stages in the development of thP is;lJ-lnil of Molokai (see explanation in text). Stage 1 shows the appearance of two sepa rate islands above sea level in Tertiary time. In stage 2 they are much enlarged, and a caldera has formed on East Molokai. In stage 3 the two islands have merged, and West Molokai Volcano has become extinct. Stage 4,

32 20' 10' 157°00' ·SO' 46·

p A C I F I C 0 C E A 4

0 10 Ml LES 5

>, >, ~ ~ ;; >

6 20 10 157 00 50 40 in late Pliocene or eurl;1· Pleistocene time, shows a new separation into two islands by submergence. Stage 5, in late (?) Pleistocene time, shows a minor renewal of volcanism on East Molokai, and stage 6 shows the present con dition ~f the island.

33 34 MOLOKAI

Molokai gradually fill the channel between East and ,vest Molokai islands and the Hoolehua Plain is formed. G. Nearly complete extinction of the East Molokai Volcano. Dif ferentiation proceeds in its magma reservoir ( fig. G, stage 3). n. B.xtrusion of the andesites of the upper member of the East Molokai volcanic series from bulky cinder cones and bulbous domes. The caldera was probably nearly filled with these lavas. 7. Gradual extinction of the East Molokai Volcano and begin ning of erosion.

LATE PLIOCENE ( ?) AND EARLY PLEISTOCENE TIME 8. Long period of erosion during which deep canyons were formed on East Molokai and smaller ones on West Molokai. Marine erosion vigorously removed a large segment of the windward coast. 9. Gradual submergence of an unknown but lai•ge amount of the island, culminating in a shore line at least 560 feet above sea level (fig. 5, stage 4), and probably as much as 1,200 feet. East and West Molokai again became two islands and the sea flooded the Hoolehua Plain. The large canyons were filled with allu vium as the streams aggraded their beds in adjustment to the higher sea level. 10. Gradual emergence with a short halt at the 250-foot level. Small patches of coralliferous limestone accumulated at the mouths of gulches on the leeward side of East Molokai at this level. East and West Molokai joined to form one island again.

MIDDLE ( ?) PLEISTOCENE TIME 11. Fairly rapid emergence with the sea dropping to about 300 feet below present sea level. The streams cut deeply into their alluvial fills and the sea continued rapidly to cut away the windward side of the island. 12. Resubmergence of the island with the sea finally halting 100 feet above present sea level. A narrow fringing reef formed along part of the south shore of East Molokai.

LATliJ ( ?) PLEISTOCENE TIME 13. ~eemergence of the island by about 160 feet exposing broad marine flats covered with "coral" sand. The wind drifted great quantities of this sand 2 miles inland up and over a 600-foot cliff oil the ~ortheast coast of West Molokai. 14. Renewed volcanic activity on East Molokai. Large v'olumes of basalt erupted at the foot of the great sea cliff to form GEOLOGY 35

Kalaupapa Peninsula (fig. 5, stage 5). About this time, lava rising under the ocean just east of Molokai exploded in con tact with sea water to form Mokuhooniki tuff cone. 15. Resubmergence of the island by about 85 feet. A narrow fring ing reef formed 25 feet above present sea level. Most of the sand dunes formed during the preceding period became lithi fieu. Some were drowned by this rise in sea level and others were cliff ed. HL Re~mergence of about 20 feet with the formation of a fringing shore bench about 5 feet above the present strand.

IlECE~T TIME 17. Further emergence to the present strand (fig. 5, stage 6). Erosion, and deposition of terrigenous sediments along the southern coast.

HISTORIC TIME 18. Introduction of livestock and agricultural development caus ing great quantities of red soil to be eroded from the uplan

ROAD METAL Most of the crushed rock used on Molokai comes from the County quarry, at an altitude of 400 feet in Manawainui Gulch (pl. 1). Several faces have been worked in dense andesite of the upper mem ber of the East Molokai volcanic series. A small quarry in dense andesite 0.75 mile northwest of Kualapuu was operated during con struction of the highway. A small quarry 0.4 mile southeast of Puu o Kahanui yielded basaltic aa clinker during construction of the private road between Umipaa and Manawainui G-11lf'h. A large gravel pit has been opened in an alluvial fan at the mouth of a small gulch 2.5 miles west of Kamalo. Many of the cobbles and pebbles are of dense andesite, but some others are basaltic. Most of the cinder used comes from a large pit on the northern side of Puu Maniniholo, a basaltic cinder cone 0.75 mile east of Kaunakakai. Cinder was quarried near the top of Waiele cinder cone, on ,vest Molokai, during construction of the road to the Kolo wharf, on the southern shore of vVest Molokai. Many other small quarries and borrow-pits have been operated temporarily along the roads during construction, or when repair materials were needed. PART 2. GROUND-,VATER RESOURCES OF THE ISLA..."N'D OF MOLOKAI By GORDON A. MACDONALD

CLIMATE TEMPERATURE, WIND, AND HUMIDITY.-The climate of Molokai is semitropical. The island lies in the belt of northeasterly trade winds, which blow almost constantly throughout most of thfl yPar. In the fall and winter months the trade winds are interrupted by periods of kona (southerly) winds, which usually last only a few days at a time. The normal trade winds are forced upward when they encounter the island mass, and adiabatic cooling commonly results in the formation of a cloud-cap over the high portion of East lfolokai, and less markedly over the top of lower 1:Vest Molokai. The southern, or leeward, slopes are largely sheltered from the pre vailing trade winds, and arc markedly drier and sunnier than thP windward slopes. Records of wind velocity are not available, but at Haiku on the neighboring island of Maui wind velocities average 11.5 miles per hour, being highest in the afternoon. On the nearby island of Oahu, during 1944, the average wind vPlority at Bellows Field on the windward side of the island, was 14.1 miles per hour, and at Hono lulu on the leeward side, it was 9.6 miles per hour. The average mean temperature decreases about 3° F. for a rise in altitude of 1,000 feet. August and September are the warmest months; .Tanuary and February the coldest. The leeward slopes have the highest daytime temperatures, and the greatest change in tem perature from day to night. Temperature records are available for only three slatiorns. They are given in the table on page 38. No humidity records are available, but on Oahu Island relative humidity is lowest in July and highest in December. During periods of light kona winds humidity reaches about 95 percent. Humidity is less on the leeward than on the windward side of the island. RAINFALL.-The mean monthly and annual precipitation at 40 stations on the island of Molokai is given in the table on page 42. The location of the stations and the areal distribution of the rain fall are shown in figure 6. Over much of the island the stations are

37 .Mean monthly aud annual temperatures at stations 011 Molokai, in l1'ahr1:mheit llPgrees, up to and including 1944 (Data furnished by U. S. Weather Bureau)

--00 Stations i:.. d ;:.... Q.) i:.. I-< ..... ~ >. Q.) Q.) . bl) 0 .... Q.) .::1 0 g .0. 0. ...., > .:: .... 'I-<

10 Maunaloa . . ~ ...... 1100 19 68.6' 68.6 69.3 69.4 71.4 73.7 74.2 75.2 74.G 73.7 71.2 70.3 71.7

24 Kualapnu ~ ...... ~ . . .. 878 38 68.41 68.3 68.4 6H.7 72.7 73.7 75.2 76.0 75.8 74.6 72.1 70.1 72.1 27 Kalanpapa ...... 50 12 71.2 71.2 70.6 71.6 73.7 75.9 77.3 77.7 77.!) 76.6 74.1 72.5 74.2 I

a Numbers are the same as those of rain gages (fig. 6). IC' 15TOO,.. 50'

·a12.14 -i5

1 ~ uu Nana • 1381 ft 9 Laau Point

Kamalo

10' 157°00' 50' Fignre 6. l\faJl of l\lolnkui. iOlokui, between ,vailau and Pele kunu Valleys. The lowest recorded average annual rainfall fa 11.7 inches, at Kaunakakai. At the summit of West Molokai the average annual rainfall probably reaches 30 inches or a little more, but records arc inadequate in that area. The driest months over the entire island are June, July, and August. The wettest months are less consistent, but in general are in the midwinter, from December to March. On the leeward coast, more rain may fall in a single kona storm than during all the rest of the year. During short periods when neither trade nor kona winds blow, mommon type of circulation caused by local heating and updraft over the land may result in local showers moving inland from the south coast. Figure 7 shows the average monthly distribution of rainfall at eight stations ou Molokai. KAUPOA GATE MAUNALOA KUALAPUU KAUNAKAKAI 8 (3) (IO) (24} (26) 7 500 ft. 1100 ft. 878 ft. 10 ft. 6 5 z 4 '3 -z <( - 2 (') a:: I :c 0 111 LL. JFMAMJJASOND JFMAMJJASOND JFMAMJJASOND JFMAMJJASOND 0 "' 0 I,_ - II ..... o-...- KALAWAO - KAMALO MAPULEHU PUUOHoK·u 10 91...- - 9 :::0 (30) - (32) (37) )> 8 RANOH 8 7 70 ft. ft. (40) 30 60 ft. 7 -z 61-1 690 ft. 6 5 5 4 4 3 3 2 2 I I' I JFMAMJJASOND JFMAMJJASOND JFMAMJJASOND JFMAMJJASOND 0 Figure 7. Diagrams illustrating the average monthly

I. Shltion 0,) .0 8 0,) > No. 0 fig. 6) Name z

1 Kamakaipo ...... 10 8 1.98 2.32 1.26 0.76 0.13 0.44 0.20 0.3G 0.6!) 2.Bl urn 1.33 13.87 2 Kepuhi ...... 40 10 2.75 0.48 1.90 1.21 0.41 0.10 o.:-n 0.11 0.41 2.94 1.34 1.28 13.24 3 Ka upoa Ga ten ...... 500 18 3.84 3.27 2.72 1.73 O.!l3 0.5G 0.52 0.75 1.11 2.61 2.28 3.51 23.8:-{ 4 Goatskin Gate ...... 450 21 3.25 2.4H 2.51 Ui7 O.H6 0.70 0.8!) 1.02 1.1!) 2.66 2.01 3.48 22.80 5 Libby No. 20 ...... 580 13 2.76 3.28 2.47 2.14 1 .on 0.60 0.(13 1.rn urn 2.46 2.24 4.07 24.29 6 Libby No. 21 ...... (145 13 2.74 3.37 2.73 2.t37 1.52 1.21 '1.33 1.61 2.00 3.2!) 2.82 4.3G 29.G5 7 Lihby No. 2 ...... (i80 17 2.94 3.23 2.85 2.26 1.26 0.77 1.09 1.32 1.45 2.53 2.33 4.73 26.7(i 8 Apalu ...... 450 10 2.87 3.43 2.54 2.27 1.rn 0.38 0.60 1.42 O.B7 2.75 1.61 2.87 22.90 9 Libby No. 1 ...... 10(10 17 2.76 3.36 2.63 2.40 1.3!) 0.58 1.04 0.!)1 l.51 2.18 2.15 4.48 25.3!) 10 Maunaloa ...... 1100 20 3.16 3.74 2.6!) 2.17 1.(iO 0.!)7 1.no 1.27 1.54 2.55 1.73 R.73 26.75 11 Manager's IIomie (Maunaloa) 1200 5 4.10 4.19 :-urn 2.irn 1.7fi 1.Hi 0. !)8 1.13 1.10 fL!{l 2.31 4.00 31.41 12 Papohaku Gate ...... 545 17 2.53 2.88 2.17 2.18 l.()1 0.40 0.80 1.0G 0.82 2.14 2.35 3.77 22.10 rn Keonelele Gate ...... 5!)0 7 4.07 0.14 1.80 1.5:1 0,(i!) 0.00 0.31 0.09 0.50 :{.24 1.65 1.45 15.47. 14 Libby No. 27 ...... 850 10 5.04 3.33 3.97 2.13 1.48 0. 80 0.!)7 0.!)7 0.72 4.40 2.42 2.80 29.0:~ 15 Mahana ...... (180 1 () 2.HG 2.mi 4.04 Uil 0.48 0.54 0.50 0.82 O.G8 4.34 1.7(\ 1.80 22.10 16 Kakainapahao ...... 450 4 1.20 3.(i2 2.H4 O.fiB O.fiO 0.27 0.04 0.14 0.51 (UH 1.Fi 3.18 15.02 17 Mant>opapa ...... ri50 4 1.2\l 4.fiO 3.04 1.37 0.44 1.:12 0.15 0.26 0.2!) l.50 1.'~6 R.01 18.43

18 Kapeelua ...... nrio 4 1.4U i 5.0!l :{.42 1.40 0.83 1.03 0.18 0.13 0.5B (Ull 1.72 3.HO 20.:rn rn Kanaio (C.P.C.) ...... (iOO Hi 2.40 ; 2.H4 3.42 1.:rn O.BO 0.2!) 0.20 0.38 0.47 2.00 2.00 2.20 18.'.!H 20 Field 501 (C.P.C.) ...... 775 13 3.82 I 3.87 5.85 4.11 3.lfi 1.44 1.24 1.5(l 1.4fi 3.74 3.17 4.5G 37.!16 21 Pekeo (C.P.C.) ...... 480 15 2.57 3.43 4.01 1.92 1.14 0.28 0.32 0.5!) 0.70 2.3(i 2AH 2.39 22.20 22 Hoolehua ...... 840 18 4.00 4.44 4.55 4.50 2.89 1.61 1.45 1.rn 1.0G 3.4(i 4.20 4.52 37.86 23 Hoolehua Routheast ...... 5(10 12 1.88 2.91 3.27 2.(H"i 1.38 0.49 0.54 0.71 0.G5 3.51 2.84 2.58 23.31 24 Kualapuu ...... 878 45 5.13 4.67 3.84 :1.17 1.5\l 1.71 0. !)2 0.1)4 1.19 1.80 3.63 4.71 32.fi2 25 Kipu ...... 1250 15 3.52 5.43 5.82 5.70 3.83 1.65 1.5!) 2.12 1.71 4.65 4.17 5.10 45.29 26 Kaunakakai ...... 10 14 1.71 2.30 2.08 0.6!) 0.64 0.01 0.13 0.21 0.24 1.54 O.H3 1.22 11.70 27 Kalaupapa ...... 50 12 ti.78 5.39 8.11 7.40 4.74 2.33 2.23 2.75 2.03 6.11 4.67 6.36 57.l!O 28 Meyer Lake ...... 2000 2 92.5 29 Poholua ...... 2400 15 3.60 '4',74 ·6.39 '5:49 ·2·.s6 'o'.7,1 'i'. ii "ijg. '1 ".si 'a".i6 's".2(i .4.. 15 38.08 30 Kalawao ...... 70 27 8.04 6.21 6.10 7.89 4.72 3.04 3.2!) 3.91 :1.23 3.65 6.62 7.83 64.53 31 Wailrnlu ...... 3700 1 ti 6.3H 7.58 10.37 5.78 4.33 1.77 2.29 3.30 2.47 4.74 5.73 7.34 62.02 32 Kamalo ...... 30 ti 1.80 1.26 2.35 3.67 1.01 1.21 2.06 1.32 l.73 1.24 1.46 6.Hfi 26.(1(1 :HI P1!lekunu ...... 5ti0 5 93.--" 34 Pohakannoho Ridge ...... 2800 1 90.= 35 Puu Lua ...... 2900 12 148.7c 3(i Mapulehu mauka ...... (i50 ti fr.27 ·8·.02 "i.20 ·8".i)6 'n'.62 .5.. 65 'njcJ °R'. 72 .4.. 87 .4.. 84 .9.. 73 92.0!) 37 Mapult>hn ...... (i(I 3!> 5.17 3.94 2.87 2.66 urn 3.11 2.!)4 2.73 2.8!) 3.18 5.16 41.47 38 Pukoo ...... !)(I 6 6.41 4.05 2.97 3.25 2.fi8 2.46 4.63 4.08 2.44 2.57 5.91 46.24 39 Halawa ...... 200 4 1.35 1.4!) 1.52 0.90 1.03 0.84 0.57 0.92 1.(i2 2.22 3.8!! 19.18 40 (i9(1 10,1 Puuohoku Ranch ...... 4.38 I 6.7:l 2.84 3.20 1.74 2.22 2.65 2.22 6.02 3.01 3.72 42.24 I • Libby- N 22 l> Gage read irngulnrly; overflow~d part cf time. c Oage read irregularly. <1 'l'hrough .Tune, l!l43; l'eeord thert>after flppears 1111l't>liahle. Annual rainfall at stations on Molokai (Data furnish<'d by u. s. Weather Bureau, plantations, ranches, and Hawaiian Homes Commission)

Station number 1 2 3 4 5 6 7 8 9 10 11 12 (fig, 6) I

<1) <1) ~ .µ c:l <1) c:l 0 ~ 0 ~ C-1 IN r1 rn 0 p. co 0 IN C c:l co\, ::I Name ·; i:::l 0 0 0 0 0 0 , ~ 1--, ::I I>, ::I i:i. ~ ::I ::Ii:: 1-3 M Altitude (feet) . ' ..... 10 40 I fiOO 450 580 645 (180 I 450 1,0(iO 1,100 1,200 545 :,, ~ Year M 1924 ...... 21.47 ...... 22.29 ..... 2ii. !)8 . .... 19.46 w 1925 ...... 14.34 ...... 16.31 . ... 15.14 'i'»>i(~ . .... 16.36 0 H)26 ...... 13.8S . . . . 16.0!) . . . . 14.70 17.77 . .... 13.BO d 1927 ...... 3'i°.49 32.88 35.55 ·2·1:;. (i4 35.06 ..... 42.99 41.15 ..... 36.39 :,, 1928 ...... 10.36 9.83 13.15 (") ...... 11.09 9.05 ..... 12.38 12.63 . ... 10.04 M 1929 ...... 30.84 32.82 34.02 30.95 34.49 ..... 35.07 ...... 30.89 U'l rn:rn ...... 24.89 22.43 26.32 2+.20 26.49 21.81 21).86 ...... 21.81 Hl31 ...... !l.81 14.59 12.92 10.29 22.70 14.78 21.87 . ... 14.78 11132 ...... 16.65 23.72 HUJS 14.45 25.15 17.78 21.04 'z"3'.i12 17.78 1933 ...... 27.51 rn.22 21.i:i6 17.65 25.74 1!J.54 24.70 22.IJ2 ·2i.iio 1 H.53 11)34 ...... 13.22 26.66 23.06 23.:rn Hl.76 29.81 16.55 27.76 27.!!6 16.55 1mm ...... 6.41 22.25 18.5!) 18.31 16.08 27.15 Hl.71l 21.H5 '2'4'.2.i 25.0(i 15.08 1H3H ...... ·fr.i2 12.51 32.66 25.05 22.82 20.rn 3fi.11 22.H8 26.78 32.2fi 3H.6ri 22.72 1 \)37 ...... ' .... 25.15 11.37 38.95 26.32 27.85 26.6\J 34.M 34.04 2H.7il :-'17.23 41.41 34.04 1!1:{8 ...... 9.60 8.45 26.64 27.05 24.60 22.13 36.48 21.:n 23.73 30.30 .... 27.31 1 !!39 ...... 21.65 21.15 28.57 25.97 25.40 38.24 32.19 35.;{2 32.44 3!-'l.21 ..... 35.32 1940 ...... 12.20 12.78 21.29 22.68 ...... 21'.86 ...... 1941 ...... 2.75 6.16 5.22 10.48 ...... 13.49 ...... 1942 ...... 17.28 24.20 25.64 32.81 ...... 40.58 ...... 1943 ...... 5.20 16.50 20.25 21.!ll ...... 27.51 ...... 1944 ...... 22.04 23.18 ...... 27.88 ......

f!a. ~ 44 .MOLOKAI

Annual rainfall at stations on Molokai (continued)

15 16 17 18 19 20 21 22 23 Sta. No. 14 (fig. 6) /~ ------co' --,:,, ...,(!) <:N <:N r;;j 1:- IN 0 0 C,.., z z :::: r;;j~ 0 r;;j "' ;:; ::i"' E 0 8-: ..::1 ~r;;j :§ z A ~ ~ .., ·;;; IQC,) <> I>, oe ~ ...... ]rJ ..... p::g '-' '-' ~ ~ (;i::;'-' ~ .... ~ ~ ~ ------(Alt. 51:lU 850 680 450 550 650 600 775 480 840 560 (feet) ------Year 1929 ...... 47.07 . ... 1930 ...... 2i.61) .... 1931 ...... 0 fr.32 .... Hi.H 3i.47 .... 1932 ...... l f'i.70 :i2·.s2 ~fa.06 18.frn; 31.18 1933 ...... i'9°.60 17.58 16.95 21.67 fr.28 3'2'.i>11 1:-urn fri.fi.4 19::M .... 15.66 11.27 14.70 19.93 14.48 31.76 17.58 3's.94 16.26 1935 .... 2·0·.35 23.73 12.54 19.38 16.69 13.94 15.96 1936 28.71 31.40 ...... 16.03 h.10 20.69 4°s". 75 i'6'.r,.9 1937 14:85 36.77 30.8fi ...... 26.85 53.81 29.52 47.13 27.9G 1938 9.98 28.94 !J.0.7tl ...... 18.83 55.62 27.33 14.89 1939 21.85 30.76 20.52 ...... 23.04 47.71 28.5i'i 4°6°.58 29.20 1940 13.62 28.34 20.70 ...... 25.37 51.88 30.73 40.51 34.6,R 1941 7.44 16.29 10.57 ...... 6.41 18.70 9.53 26.87 7.67 1942 27.29 37.67 26.07 ...... 22.45 44.55 29.35 54.05 1943 13.21 25.28 ...... 19.04 .... 22.79 30.18 i'9'.:h 1944 . . . . 24.16 10.00 ...... - - 17.58 . - .... 20.20 34.46 19.09 Annual rainfall at stations on Molokai (continued)

Sta. No. 24 25 26 27 29 30 31 32 36 37 38 39 41) (fig. 6) ------· --- ·.; .td o:j o:j i::,. ::I ::I ::I 0 o:j 0 ,d ,d .td = .td o:l o:j 0 Q) Q) 0 Name 0. o::! i::,. ::I o:j 0= o::! ::I .td ~ ...... o:j 0 t:: ,d,::l p A o:j 0 t:: ::l.td :3 0 o:j 0 :J ::I o:j i::,. ~ i:i. ,d ·a s 0. ::I .td ::l::l ::I o:j -; o:j o:l o:l o::! ~ 0 ~ ~ ::I ::li:l ~ ~ ~ ~ P< ~ ~ ;::s s ;::s P< lJ::1 P<~ ------~ Alt. 878 1,250 10 50 2,400 70 3,700 30 (feet) 650 60 90 200 690 ~ 1:.11 ------~ Year ~ 1892 44.27 Ul 1893 43.88 0 1894 32.28 d 181)5 :~7.92 ~ 1896 :rn.46 i'.1 1897 1:.11 33.92 Ul 1898 46.21 1899 1900 ii.iii 1901 40.55 1902 40.41 1903 36.34 1904 56.96 1905 23.06 64.46 1906 36.06 1907 44.45 ·1·9·.69 !°()0..3!) ·5·3·_03 1908 15.44 33.56 72.99 31.26 1909 30.12 57.24 1910 27.75 59.20 ·9·2·.10 ·4·3".io 1911 28.04 61.59 1912 16.30 1913 26.87 55.97 1914 33.46 1915 26.00 1916 59.32 iii.73 It"'- i::.n Annual rainfall at stations on Molokai ;J.,. (continued) C.

Sta. No. 24 25 26 27 29 30 31 32 36 37 3S 39 40 (Fig. 6) ------~-

·;:; c:J :::I .>:I ::i. :::I ::, ::, ::, c:J c:J 0 ::, .c: .c: .!:I ,0 c:J 0 a., C: 0 0. al ::i. ::, .::; c:J ::, ::: 0 ~ -::,.,::al 0 i,:: .<:l.Q A c:J '3 al .>:I 0 C: 0 i:., ~ ~ ::, ·;:; s ::i.::, 5. .>:I ::i.:: :::i .... al ~ '3 ~ c:J c:J c:J ....eel ::, ~ :::lc:J ~ t:i:j ~ ~ il. ~ ~ ~ ~::,- r; i:i... ::c: ~.:c. ------·------·- Alt. 878 l,250 10 :;o 2,-WO 70 3,700 30 o:.o 00 90 '.WO t\!JO (feet) ------~ ------1917 41.52 52.17 ~ 1918 44.78 0 1919 1!).55 ·4·8·.11 t< 1920 21.22 43.77 0 l !l2l 33.49 ~ 1922 20.00 'i1°.67 I>..... 1923 93.08 57.18 1924 io>io ii.98 1925 '4'i.92 26.51 l92H 35.83 l3.ll ·1·8°.i)6 1927 102.3!) 61.29 1!)28 l's°.66 46.64 43.02

1929 40.35 0 0 77.44

1930 36.04 60°.24 '2\).35 0 'ri6'.4i .39°.46 1931 26.75 49.46 · ·6·.iJo 34.[)7 5°9°.03 1)5.61 22.17 rn32 27.72 43.71 8.81 23.70 37.38 17.44 1933 25.72 33.60 13.29 19.02 36.62 ·3·6·.s1 17.75 1934 27.99 46.76 6.38 iojo 18.00 49.57 's'i.i :i 1935 24.79 32.07 8.81 44.69 23.27 44.92 40.48 1936 32.62 48.67 ll.56 67.75 28.95 52.66 42.19 46.08 1937 40.02 47.41 23.50 74.65 50.44 75.09 64.81 59.30 1938 37.71 74.88 7.26 84.00 60.05 62.12 37.12 3\i.23 1939 39.00 65.H2 20.18 Ol.04 53.65 78.34 59.79 53.34 1940 39.70 58.56 20.91 56.00 68.79 96.58 48.19 47.42 1941 20.37 46.65 3.31 33.82 34.36 57.44 28.45 38.20 1942 41.14 52.37 13.72 51.58 32.86 47.60 39.53 2r\.71 1943 31.24 42.06 7.99 29.71 46.95 77.04 46.87 1944 25.95 40.82 ll.l4 2!1.75 54.75 85.36 32.62 Plate lOA. Lithifa•d :-awl dnues ( foreg-rouml i extt·ll(lillg; li<-lo,,· SPH level uPar Ilio Pui11t. \Vl'st )lolokai. The llllllt·s Wl'l'l' forlllt!

Pia te lOB. LithiliP

The only perennial strP:1ms which reach the sea are those of the large valleys on the windward side of East Molokai, from Ilalawa Stream (pl. 11) on the east to "\Vaikolu Stream on the west, and vVaialua, Honouliwai, and Honoulimaloo Streams on the south eastern slope. The permanence of the streams on the northern slope results largely from the numerous high-level springs which issue from the dike complex exposed by erosion in the big valleys. Papa laua (pl. 13A) and Halawa Streams, and the streams on the south eastern slope, are fed largely by seepage from the swamps. Other streams reach the sea only at times of exceptionally high waterJ during and immediately following heavy rains. All of the streams are flashy, because of the steepness and higl1 permeability of the terrane, and the intermittent character of the heavy rainfall. Ko perennial streams exist on West Molokai. Several streams on the southern slope of East Molokai are peren nial in their upper courses, but during most of the time lose their water by seepage and evaporation long before reaching the coast. Such streams are the forks of Kawela and Kamalo Streams, which are fed by seepage from the swamp areas. Kawela Stream is now generally dry below an altitude of about 2,500 feet, the water reach ing the alluvial flats at the mouth of the canyon only during heavy rains, although it is reported that Kawela Stream formerly reached the coastal area much more frequently. Between 2,500 feet altitude and the Molokai Ranch intakes, at about 3,600 feet, the tributaries of Kawela Stream lose heavily by seevage. Even during dry weather the tributaries of Kamalo Stream generally form small water falls pouring into the large amphitheater-head of Kamalo Can yon, but the water sinks in the amphitheater leaving the lower 3 miles of the streambed dry. The South Fork of Kaunakakai Stream is permanent as far as the high water fall at about 1,000 feet altitude, being fed in its upper course by seepage from the swamps and in its middle course by a series of small perched springs. On the northern slope, the upper courses of Waihanau and Waileia Streams flow most of the time, the water being supplied by seepage from the s·wamps, but during ordinary weather the streams sink before reaching the sea. The intermittence of all of these streams in their lower courses, contrasted with their permanence in their upper courses, is largely the result of the streams flo-wing in their lower courses over the much more permeable basalts of the lower member of the East Molokai volcanic series, after leaving the poorly permeable cap of andesite lava of the upper member.

47 PERCENT OF TIME 10 20 30 40 50 60 70 90 I 0

PULENA STREAM

~ 251------~--,-;---...i...+---~-+--'-----1-'f-----li-+--~-~ -<( Cl Cl) z 0 ..J o,...___._...___...___...... _....___ __.....___ _..._...____.___...._._____.....__ ___.__ _.__, ..J <( (!)200H----1--+--+---+-+---..+---+--+--J..---+.I..----H---J.-----I--I 1 z PELEKUNU STREAM C>1001rtt---,r--+-~t---+-,,------,.+----:-+--+--+-i-----+-+---+--+--I

:J..J 50

250 300 350 NUMBER OF DAYS OF YEAR Figure 8. Duration-discharge curves for Pulena Stream near its junction with Wailau Stream, and for Pelekunu Stream, East Molokai. (After M. H. Carson, pl. 04, First Progress Ilept., Territorial Plan. Bd., 1080.)

Daily discharges of streams on the island of Molokai are pub lished in the annual Surface Water Supply Papers of the U. S. Geological Survey.24 A summary of records of stream flow from

2, U. S. Geol. Survey, Water Supply Papers 485, 515, 516, 535, 555, 575, 595, 615, 635, 655, 675, 695, 710, 725, 740, 755, 770, 795, 815, 835, 865, 885, 905, 935, 965, 985, 1919-1946; no. 795, p. 9, contains a list of the gaging stations and years each was in operation. 48 WATER RESOURCES 49

1917 to 1938, and a map showing the location of the gaging stations, are contained in a publication of the •.rerritorial Planning Boarct.:zn Figure 8 shows duration-discharge curves for Pulena Stream near its junction with "\Vailau Stream, and for Pelekunu Stream. Figure 9 shows an intensity-frequency curve for Halawa Stream. MEYER LAKE.-Meyer Lake (pl. 12B) occupies a shallow depres sion on the andesite lavas of the upper member of the East Molokai volcanic series, at the southeastern foot of Puu Olelo cinder cone, at an altitude of approximately 2,000 feet. It is a perched pond, held at that level by the comparatively impermeable underlying andesite and the surficial soils and weathered rock. The capacity of the natural basin ·has been somewhat increased by construction of a dam about 6 feet high. The depth of the pond varies by several feet. On October 30, 1929, it was at no point more than 5 feet. The area also varies with the stage, from about 8.4 to 10.~ acres. The pond appears to be fed entirely by surface runoff from the sur rounding drainage basin, which has an area of about 100 acres. It has been claimed that the pond is partly fed by submerged springs. Temperature measurements by M. H. Carson on October 30, 1929, at 36 islations over the pond, range from 20.29 to 20.52 degrees Centigrade, a range of only 0.23 degrees. If the pond were fed partly by submerged springs it would be expected that these springs would locally result in areas of colder water, but the measurements show no such cold areas, the range being much less than would be expected if springR exfated. On the other hand, it is reported that even during prolonged droughts the pond falls only to a certain stage, and then remains approximately constant AVERAGE FREQUENCY OF OCCURRENCE IN YEARS 20 10 5 4 3 2 I O 5 04 03 0.2 0.1 0 1000 . l1J 90 0 {!) ...J 80 0 . - 700 :E ;::E 60 0 ... 500 ,.,~ - - AV. 'L>. 40 ~ l1J 0 c-. 0::: ~ .... ~ LIJ <( 30 w (!) :::> 0:: 0 <( (/) 20 - ' '-- :c 0 0:: (/) LIJ

0 a.. 10 ~ 2 3 4 5 6 7 89 10 20 30 40 50607080100 200 400 600 800 FREQUENCY OF OCCURRENCE PER 100 YEARS Figure 9. Intensity-frequency curve for Halawa Stream, East Molokai. (After 1\1. H. Carson, pl. 68, First Progress Rept., Territorial Plan. Bd., 1939.)

. • 25 Surface water resources of the Territory of Hawaii, 1901-1938; First Progress Rept. Hawaii Terr. Plan. Bd., pp. 341-349, Honolulu, 1939. 50 :MOLOKAI

in volume. This suggests that it is spring fed. It is concluded that Meyer Lake probably is partly feu by small submerged springs and seeps. The spring ·water probably is perched on beds of poorly permeable ash, as it is at the neighboring Waialala springs and tunnels ( no. 4, 5a, 5b) and vVaikalae tunnel ( no. 6). It was at one time proposed to increase the capacity of the basiu

by construction of a higher dam7 and use Meyer Lake as a storag(• reservoir to augment the supply of water to the Hawaiian Homes Commission, or the County of Maui, during periods of lo,v stream flow. The proposal was investigated during 1929, by a Committee appointed by the Territorial legislature, and reported upon un favorably. Tests appear to indicate that the present pond loses somewhat by seepage into the underlying rocks, although the amount of loss has not been accurately determined. The walls of the basin above present water level would undoubtedly leak more than tho~w below the present water level, and furthermore the increase in head would result in greater leakage below present water level. To be used effectually, the entire basin would have to be sealed with bentonite, or by some other method. A further obstacle to the domestic use of the water is its continuous turbidity, which would necessitate filtration. Turbidity could probably be decreased or even largely eliminated by fencing the drainage areas tributary to the pond to keep out cattle.

DOMESTIC WATER SUPPLIES ON MOLOKAI Drinking water on the island of Molokai is supplied largely by distribution systems owned and operated by the County of Maui, the Hawaiian Homes Commission, and Molokai Ranch, Ltd. ( fig. 10). On Kalaupapa Peninsula the communities of Kalaupapa and Kalawao are supplied by a system owned by the Territorial Board of Hospitals and Settlement. Puuohoku Ranch and the Meyer Estate have their own supply and distribution systems. The camps

of California Packing Corporation, and T,ibhy, l\frNeill1 & Libby, are supplied from the Molokai Ranch system. Along parts of the southern coast not served by the County systems, water for domestic purposes is obtained from shallow dug wells. A tunnel 3,000 feet long leads water for the Hawaiian Home8 Commission system from ""\Vaihanau Stream, at 2,264 feet altitude, westward through the ridge to the slopes above Hoolehua Plain. The flow of ""\Vaihanau Stream for considerable periods exceeds 100,000 gallons daily, but at other times drops as low as 15,000 gallons daily. Present storage facilities of the Hawaiian Homes Commission are insufficient to provide for protracted drought periods. o 2 3 4 5 miles EXPLANATION ------County system 1-- Stream intake -·-·-·- Hawaiian Homes Commission system 0- Spring intake Molokai Ranch system ~ Tunnel intake -··-··-··- Board of Hospitals system Wei I supplying pipeline ...... Other private systems •

Figure 10. :Map of Molokni, showing the main pipe lines snpplying domestic water, and tlw eharnder of the water som'<'PS. 52 MOLOKAI

The following table shows the principal domestic water systems on the island of Molokai, and the sources from which each derives its water.

Water suppliPS of towns and villages on Molokai

flomrnunity Source of supply

Maunaloa . . . . . 979 M.R. Molokai Ranch sources.c Hoolehua ...... 1,050 H. H. C. Waihanau and Kamilo Palaau ...... H. H. C. Ioa StreamR, and spring Kalamaula ...... H. H. C. } near Kamiloloa intake (page 69). Molokai airport Do. Do. Kualapuu .. __ .. 641 l\L R. Molokai Ranch sourccs.c County No. 1 Waialala Springs, Kapuna f 25,000 Spring, tunnels 4 and 5, Kaunakakai ... 722 and Mokomoko Stream; i dug well 30. l M.R. Molokai Ranch sources.c County No. 1 Waialala Springs, tunnels f 4 and 5. Kalae ...... H. H. C. VVaihanau and Kamiloloa i streams, spring near Ka miloloa intake. IM. R. Molokai Ranch sources.c LM, E. Tunnels 4, 5, and 6. Kalaupapa . · t 447 B. H. S. Waikolu Stream; spring Kalawao .... J on east wall of Waikoln Molokai Valley. lighthouse .. 2 Do. Do. Kawela to Kamalo .... . 40 ...... Dug wells. Kamalo ...... 90 4,000 County No. 2 Dug well 42. Ualapue to Waialua .... 500 25,000 County No. 3 1\laui-type well 6, Kahana nui Stream, and spring at 1.230 feet altitude in Kahananui Gulch.d l\Iapulehu Ex I perillleuL Sta. 1<) 1.000 I H. S. P.A. Ttmnel 11. Puuohoku Ranch ...... I P. R. Waieli Stream. Halawa ...... 100 5,000 I County No. 4 Halawa Stream.

a Figures supplied in part by Molokai Ranch, Ltd., California Packing Corp., Libby, McNeill, and Libby and Puuohoku Ranch ; in part estimated from the number of service curmectlons. Population of Kalaupapa and Kalawao from 1940 census. b .Abbreviations as follows: M. R.-1\folokai Ranch, Ltd. ; H. H. C.-Hawaiian Hornes Commission ; M. E.-Meyer Estate ; B. H. S.-Board of Hospitals and Settlement ; H. S. P . .A.-Hawaiian Sugar Planters .Assn.; P. R.-Puuohoku Ranch. c Molokai Ranch sources include East and West Kawela, Karnoku, Ohialele, Luolohi, and Kalihi streams; tunnels 8, 9, and 10. • d Previous to June, 1938, part of the water for County system 4 was derived from .Ahaino Spring. Earlier, part of the water supply for Waialua came from Waialua Stream.· BASAL GROUND WATER

GE::--JERAL FEATTTREs.-Ground water moving downward through the rocks to sea level encounters sea water of greater density and floats upon it, forming a layer of fresh water, known as basal ground water.26 The water table formed by the top of this body of fresh water rises gently inland, its slope depending on the permeability of the rocks and the amount of downward-percolating water sup plied from above, but in general from 2 to 4 feet to the mile. The floating fresh water displaces salt water to an amount inversely proportional to the difference in their specific gravities, and there fore the rise of the water table inland is accompanied by a thicken ing of the layer of fresh water. This behavior of fresh water resting on the salt water in a permeable rock formation is known as the Ghyben-Herzberg principle.27 It was first enunciated for the coast of the Netherlands and certain sand islands in the North Sea, but has been found widely applicable to volcanic islands, and has been discussed for the Hawaiian Islands by Lindgren,28 W. D. and A. C. Alexander,29 Andrews,30 Meinzer,31 Stearns and Vaksvik,32 and Wentworth.33 Figure 11 illustrates the manner in which fresh water floats on salt water under an oceanic island. If g is the specific

\f'Jat~r:__t~E/e ~ M~~ sea_

2a Mi>in11,Pr, 0. E .. Ground water in the Hawaiian Islands: U. S. Geol. Survey Water Supply Paper 616, p. 10, 1930. 2 7 Badon Ghyben, W., Nota in verband met de voorgenomen put boring nabij Amster dam: K. inst. ing. Tijdschr., 1888-89, p. 21, The Hague, 1889. Horzb

34 Brown, J. S., A study of coastal ground water, with special reference to Connecti· cut: U. S. Geol. Survey Water-Supply Paper 537, pp. 16-17, 1925. 33 "'entworth, C. K., op. cit., p. 12. WATER RESOURCES 55 if the sediments were absent. Thus at dug well 30 and test hole 9 (pl. 1), only a quarter of a mile from the shore, the basal water table stands respectively 1.8 and 2.0 feet above sea level. At Mapulehu also, the water level in dug well 56 is reported to be 2 feet above sea level. Accurate measurements of head are lacking in other wells east of Kawela Gulch. In test borings 3 to 8, between Kawela Gulch and Kau11akakai, basal water appears to stand abnormally high, considering their nearness to the shore, presumably because of the confining effect of the fringe of sediments. The heads in these holes are shown in the following table. In spite of the fairly high head, the water in the area west of Kawela Gulch is brackish, because

Test borings on the island of Molokai (Data from County of Maui and U.S.G.S. files l

Salinity :: ,....._ ;..; ,....._ .::;."' -

Tl Hoolehua 398 415 1.5 60.1 624" 3.9-6.2 u. s. Geological Survey T2 Kaunakakai 314 324 1.5 2.8 29.1 7.7-8.9 County of l\fauib T3 Do. 51.5 55.5 6 12.0 255 2.50 Do." T4 Do. 15.3 19.3 6 28.0 290 2.35 do. T5 Kamiloloa 12.2 13.4 6 89.0 925 1.19 do. T6 Do. 13.8 18.8 6 74.0 770 1.13 do. T7 Malmkupaia 17.0 17.5 6 125." 1,300 1.10 do. T8 Kawela 6.4 7.4 6 40.0 420 1.22 do. T9 Do. 10.5 14.0 6 14.0 144 1.96 do.

a Average for 1945; ranges from 114 on Sept. 12, 1938, to 652 on May 15, 1945. b In bottom of uncompleted shaft. The high head and low chloride content are prob ably the result of perched water running down the hole. Small amounts of perched water were encounteret.l al t.lepthis of 107 and 174 feet. c Pumping at a rate of 54,000 gallons daily. drawdown was 6 inches. d Pumping at a rate of 55,000 gallons daily, drawdown was unappreciable, an;I salinity was 113 grains per gallon.

of the low rate of recharge. In test boring 2, at the shaft started to supply water for Kaunakakai but abandoned, the measured head is certainly raised and the salinity lowered by a small amount of fresh perched water entering the small drill-hole at higher altitudes. The head and salinity at test boring 3 are more nearly representa tive of the basal water in the area just inland from Kaunakakai. The basal water produced from many of the shallow wells in sedi mentary rocks east of Kawela Gulch is brackish, because of the nearness of the wells to the ocean. In others, some of which are equally close to the shore, the water is of better quality, owing to 56 MOLOKAI freer connection with the fresh basal water farther inland, more difficult connection with the ocean water, or both. Also, wells dug farther below the water table tend to yield water more brackish than that from wells which penetrate less deeply below the water table. BASAL SPRINGS.-Large numbers of basal springs issue along the shores of East Molokai. Many of those along the south shore are shown on plate I, but many others unduuuledly have escaped observation. All issue close to sea level, within a foot or so above it, or a few feet below it. Those which issue below sea level are difficult to locate, especially when they are small, but the presence of submarine springs is often apparent to swimmers because the escaping ground water has a lower temperature than the shallow near-shore sea water. The numerous fish ponds along the south shore of East Molokai are in themselves evidence of numerous basal springs, as brackish water is necessary to the growth of certaiu plants on which the mullet feed. Basal springs undoubtedly are numerous along the north and east shores of East Molokai also, but the rough and precipitous nature of the coast makes them difficult to observe. Very brackish basal springs occur along the shores of West Molokai. Discharge and salinity measurements are available for only a few of the basal springs. Loiloa Spring, at Pukoo, issues from alluvium near the base of a spur of basalt. The owner, Mr. E. K. Duvauchelle, reports measurements made about 1910 showed the discharge to be approximately 7GO,OOO gallons daily. At low tide on September• 22, 1945, the salt content was 18.7 grains per gallon (194 parts per million of chloride). The large pond just east of the mouth of Kawela Gulch is fed by basal springs which issue in the pond. At low tide, on October 15, 1945, the overflow of this pond was estimated to be about half a million gallons daily. The salt content of the water in the pond near one of the springs was 23.5 grains per gallon (244 parts per million of chloride). At Kokokahi, 2.8 miles northwest of Kaunakakai, a spring issues from emerged coral ..reef of the 5-foot stand of the sea. It issues largely beneath the water of a mangrove swamp, and the discharge is difficult to estimate, but is probably in excess of half a million gallons daily. The water has a salt content of 74.7 grains per gallon (775 parts per million of chloride). A spring discharging into a fishpond 0.7 miles N. 39° W. of Kalaeloa Point is stated to have a flow of 20,000 to 30,000 gallons daily. Its salt content at low tide on October 15, 1945, was 14.9 grains per gallon ( 115 parts per million of chloride) . A spring 0.2 mile farther east, at the head of Keawanui fishpond, was dis· charging on the same day about 70,000 gallons daily at low tide, WATER RESOURCES 57 with a salt content of 7.9 grains per gallon (82 parts per' million of chloride) . WELLs.-A great number of shallow wells have been dug along the southern coast of Molokai. All of these produce water from the basal zone of saturation. Most of them obtain their water from the sedimentary rocks, but some penetrate the sedimentary cap and produce from the underlying volcanic rocks. The table on page 58 lists 61 dug wells now in use, or abandoned wells on which informa tion is available, with their depth and salinity. The locations of the wells are shown on plate 1. Many other dug wells have been abandoned, and no data on them is now extant. The position of a few of these is shown on plate 1. Nine of the wells on Molokai are of the Maui type.36 These consist of a ghaft g1rnk to, or 8lightly helow, the basal water table, and one or more infiltration tunnels extending outward from the shaft to skim fresh water from the top of the basal zone of saturation. Data on these Maui-type wells are given in the table on page 60. All of them have vertical shafts. In 1938 construction of a Maui-type well was started by the W. P. A. for the County of Maui, at an altitude of 314 feet in Kaunakakai Gulch, on the advice of H. T. Stearns, to supply water for Kaunakakai. However work was terminated when the shaft was only about 40 feet deep because W. P.A. lacked equip ment to complete the work. It was entirely in coarse bouldery alluvium. The Kanoa, Conant-Kawela, and Breadfruit-tree wells were dug for the American Sugar Co., under the supervision of Mr. E. E. Conant, in 1920 and 1921. The Conant-Kawela well (Maui-type well No. 4, pl. 1), has two tunnels, the eastern one 37 feet long and the western one 192 feet long. It is reported that water was encountered which entered the tunnel at too high a rate for the pumps to handle, necessitating the ubundonmcnt of the ex cavating equipment in the tunnel. Pumping at a rate of 3 million gallons daily lowered the water level only one foot. The County of Maui is now cleaning out this well for use as part of the water sup ply for Kaunakakai.

86 Stearns, H. T., and Vaksvik, K. N., Geology and ground-water resources of the island of Oahu, Hawaii: Hawaii Div. Hydrography, Bull. 1, p. 824, 1085. 58 MOLOKAI Dug wPlls on Molokai

....,c., _..,~ Salinitya c., I c., No. Land c., 'H s __, NaCl Cl. Use Remarks (pl.1) Division -~ "O ~ ;.;o~~ _.., c., ..i::::...., (gr. (p.p. ~'.;:l Q,.) .=.. m:) c., I ga1.) ~~- c;l __,.... ~

b I :Kaluakoi 8 10 150 1,558 Abandoned 1 C h 10 30 C Do. 2 Do. 1, do. 35 40 403 4,187 do. 3 182 1,890 Stock Halena well 4 do. 8 11 do. 29 31 466 4.840 Stock l\loomomi well 5 Kolo well 6 do. 7 9 212 2,200 Stock do. 11 15 202 2.100 Stock "\Yaiaka11e well 7 Kukuku well 8 do. 3 6 233 2,420 Stock Punakou well 9 do. 8 9 156 1,620 Stock 10 Iloli 1 6 95.6 993 Stock Iloli well 11 Kaluakoi 23 25 770 799 Stock Puu Pili wen 12 Naiwa 6 7 58.8 610 Stock Palaau well 18 Do. 2 4 89.8 932 Stock Ooia well 14 do. 15 16 61.5 639 Stock Oliwai well 15 Kalamaula 5 15 54.9 570 Unused Kalamaula well h 16 Kaunakakai 18 20+ 74.0 769 Abandoned 17 Do. 8 11 115 1,190 Irrigation Hotel well 18 Kupaakea 10 14 fiK4 710 TTnm,ed Head 1± foot 19 Do. 0 2.1 3.56 93.0 970 Unused Head 1.24 feet 20 do. 2 ,:>•) 65.3 678 Stock 21 Kamiloloa 2 4.5 58.8 610 [rrigation (Govt.) 22 Do. d18.0 18.7 60.0 620 Stock Head 1.25 feet 23 do. d8.2 8.4 73.0 760 Irrigation Head 1.17 feet 24 Kamiloloa d9± 9.8 106 1,100 Unused 25 Do. d10.3 11.0 94.0 980 Stock Head 1.17 feet 26 do. <113.5 13.9 279 2,900 Abandoned Head 1.16 feet 27 Makakupaia <111.8 12.6 116 1,210 Stock Head 1.14 feet 1 28 Kawela ' 13.9 14.6 22.0 230 Stock Kaokini ·well ; head 1.39 feet 29 do. 9 10 22.4 232 Stock 30 do. 17.1 19.0 3.3 34 Domestic Head 1.77 feet 31 do. 14 15 3.1 32 Domestic and irrigation 32 :Makolelau 8 10 51.5 535 Irrigation and stock 33 do. 17 18 38.6 400 Stock 34 do. 4 5 40.5 420 Stock 35 Kapuokoolau 12 14 42.9 445 Irrigation 36 Do. 11 15 29.8 310 Stock 37 Kamalo 7 7 42.9 440 Stock 38 Do. 19 20.5 7.9 82 Irrigation and stock 39 do. 27 27 8.9 92 Stock 40 do. 19 21 22.2 2~0 Trrig:1 t.ion 41 do. 17 18 6.6 68 Irrigation 42 Wawaia 41 41.5 7.5 78 Domestic County Kamalo wene 43 Puaahala 16 19 58.8 610 Irrigation 44 Do. 8 8 4.5 47 Domestic and irrigation 45 Kaamola 6 6.5 7.9 82 Domestic and stock WATER RESOURCES

Dug wells on Molokai-(continued)

.....,., ...... - Salinity" C,) :: ~ I No. Lund =,...... ,-_ c;:: i ·- _, 4- (pl. 1 t DiYision ~Et '-' NaCl CL Use Remarks f5~ .::::...... (gr. (p.p. gal.) m.) ~:: f..... 4(i KPawauui rn 20 5.0 ri2 Domestic and f I irrigatiou 9") 47 West Ohia Hi ! Hi 3.1 Irrigation Goes dl\\" Oil ··- pumping 48 Manawai 90 '>_,- 5.,- 70 Irrigation 49 Ualapne -··-! (; 20.0 20.'; lrrigatiou 50 Do. 8 11 18.8 rnri Irrigation ')'> r- 51 Kaluaaha 2~~ -,J.• ) 14.9 155 Do. fi2 Do. 20 22 14.3 148 do. 53 do. rn 22 11.7 122 Irrigation 54 do. 22 23 15.4 160 Do. 55 Mnpnlchu r, 11.r. 12.6 131 Irrigatio11 56 Kai11alu 20 20 4.2 44 Stock 57 Waialua 7 8 29.8 310 Irrigation 58A Kapulei 14 16 2.4 25 Domestic 58B do. 15 17 2.1 22 do. 59 do. 15 16 2.2 23 do. 60 do. 12 16 3.3 34 Irrigation

a Except where otherwise indicated, salt determinations are by S. ·wong, Hawaii Div. of Hydrography. hReported by W. Lindgren, U. S. Geol. Survey, W. S. P. 77, pp. 37-47, 1903. c Too salty to m,e. <1 Data from County of Maui. Salt determinations by L. T. Bryson, Honolulu Boar

Syi:sternatic water-level measurements have been made by Mr. Herbert 1Yilson, of the County of Maui, at Maui-type wells 1 (Conant-Kaunakakai) and 6 (Ualapue), and dug well 42 (County Kamalo well), since 1938. The records have been published in tlw annual water level reports of the U. S. Geological Survey.27 Graphs of tlH, water-table fluctuation in these three wells are shown in fig-nreB 12 and 13. Sf'veral wells were drilled for the American Sugar Co.) during the years HtOO to 1902. All were abandoned because of the high salinit~· of the ,vatcr. The positions of the wells are shown on plate 1, and in figure 14. Information on the wells is listed in the table on page GJ. The information on these Jong-abandoned wells is from the report b~· Lindgren.:is A well is reported to have bf'e11 drilJed by

37 l1. ::-. Geol. Survey, Water Supply Papers 845, pp. 62-63, 1939; 886, p. 87, 1940; !n1. r,. 144. 1941; 941, p. 111, 1943; 991, pp. 194-195, 1945. 38 Lindgren, W., The water resources of Molokai, Hawaiian Islands: U. S. Geol. Sur vey. Wlltn Supply Paper 77, pp. 37-47, 1903. 1\Iaui-1 n1e wl'llr, mi the island of Molokai

Salinity 'H No. Land 0 ,,-._ ,_; Owuer U:,;p (vi. 1) NamP c;i Division ....., M Q;... z'-'~ M

1 Conant-Kannakakai Kaunakakai 28± 27.3 1 50 50.0 520 l.2G- :Molokai Haneh Unuse

a Pumped for 4 weeks at a rate of 1.5 million gallons daily dur the water. The eastern tunnel is 37 feet long. Mr. D. C. Derby, of ing 1920, with a drawdown of 18 inches. Salt content was stated Libby, McNeill, an Reporte,1 by Mr. Couu n t (op. cit.) to have heen vumped at a Stated hy l\.lr. Conant (op. cit.) to have developed more thau rate of 3 million gallons daily, with one foot drawdown. The tnn 650,000 gallons of water daily. t1PI n111ning wt•Rt from ll11~ shnft is 192 fN,t long, arnl yiel

::\kCandless Brothers near Kamalo, for the Hawaiian Gove1·11ment, iu 1883.::o It~ location is no longer kno-wn. The wat("r is said to have been salty, and the well was probably drilled too deep. Drilled "~en 1, on the northwestern slope of "\Vest Molokai, \Vas drilled for Libby, McNeill, & Libby during 1945. Basal water ·with a temperature of 93 ° F. was encountered 5.6 feet above sea level. 1Yith the l)ottom of the hole 12 feet helow sea level, the salt cunteut of tl1e water was 19G grah1s per gallon (2,040 p.p.m. of chloride). Upon dPepening the hole to 32 feet below sea level, the salt content increasl'd to 279 grains per gallon (2,900 p.p.m. of chloride). A par tial chemical analysis of the water is given in the table on page 78. The temperature of the water is much higher than the normal tem pe1·atnre (70°-85° F.) of ground water in the Hawaiian Islands. The high temperature is tentatively attributed to heating by hot vokanic emanations from greater depths. Drilled well 15, at Kualapuu on the western slope of East Molokai, was drilled for the California Packing Corporation during Febru ary. 1946. Basal water was encountered 10.5 feet above sea level, "ith a salinity of 95 grains of NaCl per gallon (987 p.p.m. of Cl). The head is a little higher than would normally l)e expected at that distance (2.2 miles) from the sea. The lateral movement of the basal water is probalJly impeded by poorly permeable rock, possibly dikes. as the locality lies on the westerly projection of the dike complex exposed in "\Vaikolu Valley. The rate of recharge is too low to keep the basal water fresh. The salinity undoubtedly results partl~· from diffusion upward from the salt water beneath, but probably also partly from carrying downward during rains of salt deposited by spray on the soil and vegetation. During October 1946 a pump was installed. Pumping at a rate of 200 gallons a minute, with a drawdown of five feet, resulted over three weeks time in a gradual lessening of the salt content to 36 grains per gallon. It is believed that removal of brackish water by pumping caused the inflow of fre1Sher waler from the regions of higher rainfall nearer the top of East Molokai Mountain. Test boring 1 (T 1, pl. 1), 1.5 inches in diameter, was drilled with a diamond drill for the U. S. Geological Survey by J. M. Heize1\ during 1938, on the Hoolehua Plain near Molokai airport. Data are given in the table on page .55. Systematic head and salinity meas nrements have been made at this hole since ·1938, by Mitchell Pauole and Solomon Hanakeawe, of the Hawaiian Homes Commission, and

3• McCandless, J. S., Development of artesian well water in the Hawaiian Islands, p. 6~- Honolulu, 1936. .., (>- :uoLOKAl

JAN FEB MAR APR AUG 5 10152025 510152025 5 !Ot52025 5 10152025 1938

U6 0.4 12 1.0 0.8 0.6 0.4 0.2 o.o U..U..U..J..1..J..1..J..Ll-'--'....l..l..J..JU-l-:-J-'--'....1..1....1..l..WL..l..J...J..J....l..l..J...l..J...l..L...;L.j~;-1-J...J..J.....LU...U...W...1...WI...Wl-LL..J..W...W..u...:...i....cl MAUI-TYPE WELL I (Conant Kaunakakai Well)

JAN FEB MAR APR MAY 5 10152025 5 !0152025 5 10152025 5 10152025 510152025 1938

DUG WELL 42 (County Karnalo Well) Figure 12. Graph showing the fluctuation of water level in Maui-type well 1 {Conant-Kannakakai well) and dug Wl'll 42 (Count:, Kamalo well). from 1938 to ·1lHJ. WATER RESOURCES

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV 5 K>!52025 51015202!> s 1ors2025 510152025 510152025 510152025 s 101s202S S·1o1S202S 5 10152025 5 10152025 s 101s2025 1938

MAU I-TYPE WELL 6 (County Ualapue Wei I)

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC s 101s2o~s s 101s2025 s 1.01s202S s 10152025 s 101s202S s 101s202S s 101s202S s 101s2025 s ~1o~1s2~o'.::25I!5!'0!1~_2r:r9.r:T';i::-_j;s;;i;;,o;J;;:s2::.Co;'j;2S'F"a;;;;"~ 1938 ---'?---'?--

1942

TEST BORING I (Near Airport) Fig-ml' 13. Graph showing the fluctuation of water level iu :\Iani-type \Yel'. ,; (County Ualapue well) and test boring 1, from Hl88 to ln45. T>rillPd wl'118 on the islarnl of Molokai' - ·-----, -~----·····--·--~ -·------· ------. -·------·--·~------~_..., Q.) Salinity Q.) No. 'H ;..,~ Q.) Q.) 00 '--' _...., Q.) ( !)l. 1) ':i ~_...., Lnud Division Q.) .d U8e Remarks ::I Q.) .d NaCl Cl Q.) ... 'H 0. s'"' § Q.) ~.s (gr. gnl.) (p.p.m.) --1 --- 0 ~- 1 Kalun koi ...... rmn fi-10 6 279.1' 2,900 ? Head G.(m feet; water warm ( 93° :U'.) 2 Hool<'hna ...... 12fi ') 140 12 102. 1,060 Ahnrnloned •) Naiwn ...... 22 7-1 12 86.0 893 Do. 4 Dt). .... ' ...... 23 73 12 86.0 893 do. 5 <1o...... ,...... 22 250 ...... • ...... do. 6 do...... iiO 12fi ...... C ...... do. 7 do...... 37 70 12 90.0 !)35 do. 8 Kalamaula ...... 20 60 12 102.0 1,060 do. !) Do. 27 343 12 ...... " ...... do. lOA Kmmakakni ...... 22 60 12 lOB 86-96 893-997 do. Cm1efi<•l

" Data for wells 2 to 14 from Lindgren, "'·• U. S. Gtol. Survey, g Increased to 2(; grains per gallon after pumping 12 hours at n Wnter Supply l'nper 77, pp. :i8-!7, 1903. r::te of l million gallons daily. 11 b With tlle hole at a <1q>th of Gl7 feet, ::mlinity was 1\Hl gruins Jncr1•ai,;e(l to G+ grains rer gallon after 1mmping 30 days at a per gallon (2,040 parts per million of chloride). nte of 2% million gallons daily.

c Reporterl to be close to ,ea water. J A pit and two i,;hort tunnels were opened at this Hite, the bore hole lwing within the pit, and pumped at rates up to 4 million gal <1 i:"rreater than 100 grai11H per gal101.. lm1;,

rnte of 1 million gallom;

published annually in water level reports of the U. S. Geological Survey.4 ° Fluctuations of the ·water table are shown graphically in figure 13. Test boring 2 ( T 2, pl. 1). of the same diameter, was drilled at the uncompleted shaft in Kannakakai Gulch for the County of Maui during 1939, by J. M. Heizer. Small amounts of perched wate1· entered the hole at altitudes of 157 and 140 feet above sea level. The head of the basal water measured in the hole ranged from 7.7 to 8.9 feet above sea leve~, and the salt content was 2.8 grains (29.1 parts per million of chloride). The head is abnormally high and the salinitv abnormallv low for this area. undoubted], because of the • t/ ; L perched water entering the hole at higher altitudes, building up the head in the hole, and diluting the basal water. Test Borings 3 to 9 (T3-T9, pl. 1) were drilled during 1945 for the County of l\laui, b,r ,v. M. Mullin, as part of an investigation of

Contour interval 50 feet

PACIFIC OCEAN ~ Figur(• 14. Map of Kaunakakai and vicinity, showing the positions of aban dorwd drilled wells. Twelve wells lie on the line between well 100 ( Settlement

Wen I and well lON (Deep Well), spaced too closely to be shown on the map. ,v(~m- 12A to T were the so-called Risdon Wells.

" r. S. Geol. Survey, "'ater Supply Papers, op. cit. W .\TER RESOL'RCES 67 nwans for developi-ng a new source of water for Kaunakakai.41 Data on conditions at these holes are shown in the table on page 5;3. The head and salinity at test boring 3 are believed to be much more nearly representative of ground water conditions in the area just inland from Kaunakakai, than are those at test boring 2.

PERCHED GROUND WATER

'! \\'ent·worth, <:. K., unoublished report to Count~· of ~laui, 1945. Kamalo

0 2 3 4 5 miles EXPLANATION ~:::::::::::::::::i I III 111111111111 t•.••.•••..•.•..••l II II II 11111111 11 Fresh basal water Brackish basal water Fresh water confined Small amour:ts of fresh floating on salt water floating on salt water at high level by dikes water perched on ash beds Figure 15. Map of Molokni, showing ground-water areas. WATER RESOURCES 69 level farther down the canyon. A tunnel 70 feet long ,vas dug pre vious to 1902 along the contact of the alluvium and the ande site, following nearly beneath the stream bed, but failed to increase the discharge. The inner 50 feet of the tunnel have caved in. It is pos sible that further tunneling, following the water back to its points of leakage from the volcanic rocks, would increase the discharge, but it appears doubtful whether the increase would ue sufficient to warrant the expense of tunneling. Kapuna Spring never dries up, although at times the discharge becomes very small. The maximum. minimum, and mean daily discharges of Kapuna Stream for the years 1940 to 1945 are shown in the following table. The maximum

Daily discharge in gallons of Kapuna Streama

::\Iaxirnnrn Minimum Mean

1940b 240,000 10,000 30,000 1941 100,000 10,000 30,000 1942 3.800.000 10,000 96,000 1943 130.000 10,000 31.000 1944. 180,000 10.000 19.000 U)45 420,000 3,000 15,000

a Data from U. S. Geol. Survey, Water Supply Papers 935, p. 71, 1943; 965, p. 66, 1945 ; and unpublished files. The low stage flow is entirely discharge of Kapuna Spring. b July to December only. discharges iuclude a large proportion of surface runoff. The mini mum discharges are entirely spring flow. The actual spring dis charge probably ranges from 10,000 to about 25,000 gallons daily. A small spring issues from andesite in the south wall of Luolohi Gulch, about 30 feet above the pipeline trail, 2,000 feet west of tunnel 9 (pl. 1). It appears to be pP.r<>herl by a thin bed of ash. On September 29, 1945, the discharge was about 300 gallons daily. A spring issues from andesite, above a bed of red ash in the south eastern side of a plunge pool, 300 feet upstream from Karniloloa intake of the Hawaiian Homes Commission. It is shown on plate 1, 0.4 mile northwest of Kaulahuki hill. During dry weather the entire stream flow at Kamiloloa intake, or about 40,000 gallons daily, is supplied by this spring. Several small perched springs occur along the upper course of the South Fork of Kaunakakai Gulch, from about 2,450 to 3,150 feet (pl. 1). They issue in the lower part of the northern bank, at the base of the andesites, which here rest on 3 to 5 feet of red ashy soil. Near the westernmost spring the stream flow was estimated on October 9, 1945, during dry weather, to be about 75,000 gallons daily. 70 l\IOLOKAI

Above the easternmost spring, at the crossing of the abandoned Kawela pipeline, the stream carried about 40,000 gallons a day of water of pale bro,vn color, derived by seepage from the swamps a short distance upstream. The spring discharge on that day was. therefore, about 35,000 gallons. On January 5, 1946, following a further period of three months of mostly very dry weather, the sh-earn flo,v below the springs was measured by the waterman of Molokai Ranch as only 12,000 gallons daily, all of which probably came from the springs. Haleloulu Spring is situated 0.9 mile southwest of Pun Kolekole~ 1war the western boundary of the l\fakolela u land diYision {pl. 1) . Three small springs issue close together, from clinkcry andesite aa 0 to 10 feet above a bed of ashy soil 1 to 2 feet thick. The. soil rests on a thick bed of clinker, decomposed at the top, forming part of tlw edge of a lmried andesite cinder cone. On October ::!, 1945, the total spring discharge was about 20,000 gallons daily, of which about half was recovered and led by pipeline to a cattle trough. During wetter weather, from June 3 to December 11, 1937, nine measurements by the Molokai Ranch showed the total spring discharge to range from fi9,7GO to 24,170 gallons daily. On the west bank of Kahananui Stream, about 100 feet down stream from the County intake at 1,230 feet altitude, a small spring issues from basaltic aa clinker. An excavation about 5 feet deep and 6 feet high serves as an intake, and the water is led into the County's "Galapue pipPline. On February 25, 1939, the spring dis charge was estimated by H. T. Stearns to be about 2,000 gallons daily. The ,Yater appears to be perched by a dense bed of lava. Near the trail from l\fapulehu to \Vailau Valley, about a quarter of a mile south of the crest, a small spring issues from the andesite. The environment is swampy, and the water is swamp water, locallJ· perched on the poorly permeable andesite. Many such springs and seeps issue in the swampy upland areas, feeding the perennial por tions of the streams, but they are in general too poorly defined to show on plate 1, or to warrant individual description. The spring n(~ar the "'\Vailau-Mapulehu trail is discussed only because it is habitually used as a source of drinking water by persons traveling the trail. Ahaino Spring is situatPd at ahout 1,240 feet altitude, in land belonging to E. K. Duvauchelle in Ahaino 2 land didsion. The water issues from a clinker bed between two massive layers of andesite. It is probably perched by a thin layer of ashy soil, although no ash is visible at the spring. On February 24, 1939, H. T. Stearns esti mated the spring discharge to be about 9,000 gallons daily. A short WATER RESOURCES 71 tunnel at this place would permit the development of all of tht· water underground, but the yield of the spring would prulJalJl,v nor be materially increased. Ahaino Spring was formerly used as a source of water for the County's Ualapue system, but this use was discontinued in June 1938. On the eastern ,vall of Pelekuuu Valley. half a mile to a milt~ from the beach, a series of spring~ issues from basalt at the top of a hed of decomposed vitric tuff 4 to 8 inches thick. During September, 1933, the total discharge of these springs was estimated by IL T. Stearns to be about one million gallons daily. Near Malahini Cave, in the eastern b1·anch of ·wailau ValleJ\ a small spring issues from ancient alluvium. Although the water i:-; locally perched in the alluvium, it is probably supplied by leakage from the dike complex. TUNNELS DEVELOPING PERCHED GROUND ,vATER.-All but one of the tunnels yielding perched ground water were driven in andesites of the upper member of the East Molokai volcanic series. In most, the water is seen to be perched by thin beds of ash or ashy soil. The table on page 73 contains the principal data regarding the tunnels. A long tunnel from ,v::iilrnrnrn StrPam to thf' headwaters of the llanawainui drainage was constructed entirely for the purpose of transporting water from vVaihanau Stream, and develops no perched ground water. ':runnels 2a and 2b, 0.3 mile south of Pun Lua, yield a small amount of water during wet weather, but dry up completely during droughts. The tunnels are caved in and inaccessible. The portals are in alluvium, but the tunnels are probably mostly in andesite. A spring formerly existed at this locality, and it is reported that construction of the tunnels did not increase the discharge.42 Tunnel 11 was driven at the site of a formr•r spring, at the toe of the ridge between the two major forks of :Mapulelrn Stream. Tunneling probably did not greatly increase the discharge. 1.'he water issues from basalt aa clinker, and is probably perched bJ' the underlying dense bed of basalt. The source of the water is probably leakage from the adjacent dike complex (see pages 72-77), but ~ome or all of it may be derived from seepage from the sh-earns of the em,t .and west forks, in the beds of both of which the clinket layer is exposed. Both streams are perennial near tlwir heads, fed by seepage from the swamps, and both lose water rapidly in the half mile above the tunnel. Tunnels 4, 5a, and 5b, and two nearby small springs, at "\Vaialala, all yield water from andesite. No ash or soil bed is exposed in the

• 2 Lindgren, W., op. cit., p. 29. 72 l\IOLOKAI tunnels, but it is probable that such a bed, similar to those exposed in tunnels 3 and 6, is present and responsible for the perching of the water. The total discharge of the tunnels and springs is measured at a gaging station, and the records are published by the U. S. Geological Survey.43 The maximum, mrn1mum, and mean daily discharge for the years 1940 to 1945 are shown in the following table.

Daily discharge in gallons of Waialala springs and tunnels"

Maximum l\Iinimum Mean

19-!0h 35,000 18,000 2fi,OOO 1941 96.000 21,000 30.000 1942 275:000 21,000 43,000 1943 47.000 17,000 27,000 1011 64,000 12,000 20.000 1945 43,000 4.000 10,000

a Data from U. S. Geol. Survey, Water Supply Papers 935, p. 69, 1943; 96u, p. 64, 1945 ; and unpublished files. b September to December only.

WATER CONFINED AT HIGH LEVELS BY DIKES Within the rift zones of East Molokai Volcano, the lavas are cut by very numerous dikes, representing the chilled fillings of fissures which fed lava flows, and other fissures which failed to reach the surface. Most of the dikes are essentially vertical, though some are inclined. A few pass into sills, which are essentially parallel to the bedding of the lavas; that is to say, nearly horizontal. In the eastern part of East Molokai Volcano most of the dikes trend roughly eastward. In the western part, most of them trend about N. 65° W. In ,vaikolu, Pelekunu, and to a less extent in the eastern part of Wailau Valleys, both these trends are represented, and it appears probable that the east-west trend extends as far as the Hoolehua Plain. In the area between the upper courses of Kamalo and Kawela Streams the trend is probably southeasterly. The dikes are most numerous in a band about two miles wide, known as the dike complex. At the edges of the dike complex the abundance of dikes decreases gradually, fewer and fewer dikes being encountered as one travels outward from the old rift zones of the volcano. The dikes range in thickness from less than a foot to about 15 feet. The rock of the dikes is generally dense and nonvesicular, and although the dikes are generally cut by abundant joints roughly

•3 Carson, M. H., Surface water supply of Hawaii: U. S. Geol. Survey, Water Supply Papers 935, 965, 985. Tunnels driven for perched ground water in Molokai

.µ ..., Q.i -- Q.i Q,) ~ Q,) '-' .'+-, ,..._ '-' No. Owner Location Q.i >. Perching formation "O ,Q ~ ..., "O (pl. 1) Name ...,:= bj) "O ...... µ ~ a., Q.i Q,) - '"' :;J 1-=l ~~

1 Waiakane Molokai Ranch Co. S. fork of Kapale Gulch 1,000 40 500 Ash bed in upper member of East Molokai volcanic seL·ies. 1\ 2a Puu Lua Do. 0.3 mile south of Puu Lua 1,230 ... 0 0 • o a O I• o O O O O IO O O o O o 0 2b Do. do. Do. 1.230 . ..a 0 ...... Ash hed in upper member of 3 Waipunahonu do. 0.4 mile east of Pun Lua 1,550 155 200 ~ East Molokai volcanic series. ~ i-3 4 Waialala Meyer Estateb Waialala Gukh, 35 feet west 1,600 ARh lwd ( '?), in up1>er member el of road to head of Kalan- 100'} of East Molokai volcanic ~ papa trail 25,000d S('rieR. l:d el 5a Do. Do.b no., 100 feet east of the road 1,680 40 Do. '(fl Do. 0 5b Do. Do.b Do., just east of tunnel 5a 1,680 3 (j 6 Waikalae Do. Waikalae Gulch, 0.65 mile S. 1,780 327 20,000 A.Rb l)p{l in upper memlwr of l:d East Molokai volcanic seL·ies. l.l 73° W. of Puu Olelo el 7 Waihii Molokai Ranch Co. Waianui Gulch 1,650 100c 1,oooe Do. '(fl 8 Waiiole Do. Waiiole Gulch (north fork of 2,200 60 20,1)00 Do. Kahuanui Gulch) 9 Luolohi Do. Luolohi Gulch 2,780 soor 30,000 Do. 10 ...... Do. Do., 350 feet upstream from 2,800 50 300 Do. tunnel 9 11 Mapulehu Hawaiian Sugar Ma1mlehu Gulch 650 60 ~5.000 Dense bed in lower member of Pla11ters Assn. East Molokai volcanic sel"ies.

a Caved In and inaccessibl~; reported as short by Lindgren, U. S. e Unused. Geol. Survey Water Supply Paper 77, p. 29, 1903. r Length reported by Lindgren, op. cit., p. 30; now caved 100 feet b Water sold to County of Maui. from portal, but nearly all the water was developed in the first c Partly caved in. 100 feet. d Includes discharge of two adjacent small springs. 74 MOLOKAI normal to the dike walls, they are on the average much less permeable than tlw vPsif'nlar anrl par·tly clinkery lava flows between them. Thus in the dike complex the intersection of numerous dikes of different trend gives rise to a condition somewhat resembling .1 honeycomb, in ·which roughly vertical prisms of moderately perme able lava rock are separated by relatively impermeable dike parti tions. Rain water sinking into the rock at the tops of the permeable compartments tends to accumulate in the compartments, its latenll movement being prevented or retarded by the dikes. "\Yithin th«· permeable compartments the water accumulates to a level at which leakage through the confining dikes equals the recharge. The cmnn lative effect of the dikes results in the water level in the inner com partments of the rift zone being higher than that in the oute1· compartments, the rise of the water table being by steps, as shown in figure 16. Locally, the water in the inter-dike compartments ma~· be resting on salt water, and in counterbalance with it according to the Ghyben-Herzberg principle (page 53). More commonly, how ever, the great increase downward in the abundance of intrusive rock results in the rock at depth being essentia11y impermeahh., holding up the fresh water in the inter-dike compartments and shut ting out the salt water. ln most places, therefore, the higll-levPI water in the dike complex is actually perched on pool'ly permeahh, intrusive rock. In --west Molokai Volcano, at altitudes above sea leveL the dike complex appears to be much less well developed than iu the East lVlolokai Volcano. Drilled well 1 (pl. 1) lies within, or close to tlw edge of, the northwest-trending rift zone, yet the water is brackish and stands at an altitude corresponding to the normal basal zone of saturation. Apparently at that location, at least, the concentra tion of dikes is insufficient to shut out the sea wate1·, or to prPn>Bt the easy lateral escape of fresh water. Possibly in thP dcinit.'' of Puu Nana, where the northwest and southwest rift zones intersect, or for a short distance southwest of Puu :Kana along tlw Honthwest rift zone, inter-dike compartments may confine fresll water. How e,-er, the rainfall, and consequently the recharge, is so low in thi:-; area that it is not likely the water is held very far above sea level. Some leakage through the dikes always occurs, and with low r(~ charge not much leakage is required to allow the water to esc.ip~ laterally instead of accumulating to high levels in the inter dike compartments. For these reasons, no area of water confined at high leYels by dikes is shown on ·west Molokai in figure 15.

"\Vailau, Pelekunu1 and "\Vaikolu Valleys are great notches cut into the dike complex of East :Molokai Volcano. These notches sene to l'lnk l~A. Yi<·w of tlH• Pa:-;l(•t·11 :-:lop.- 1>t' \\'t•:-:t \lolokai from l'u11 o l'ipika; :-:l10wi1.g· :-:tqJ-fanlt :-:nrp:-: 011 thP ll'ft, th<· ;\lahatltl gTalH'll iu tht• Cl'll!PI'. Hlld IWO :-:mall tilt<·d fa11lt hl1wk:-: m1 tlw right. 'l'lw rigllt-ha11d b!rn·k i:-: l\'ailrnua hill. Photo hy U. A. :1ln<·dorntld.

Plitt(• l~B. l\ll•ypr L:llw.

!'late t:m ( rigl1t l. ( lhi:1!(,Jp ~1 rP:trn. (i('Se<'!Hli11g hr n Sl'l'iPS of wakr falls 11nd pl11ng<•pools into thP hPad of "·nilrnlu YallPy, East Molokai. i'l10to li,v IC ,J. HnkPI\ WATER RESOURCES 75 drain the adjacent inte1·-dike compartments. Many springs occur ill these valleys, owing to the escape of water from hehinil ilikes. It i"' to these springs that the streams largely owe their perennial charat ter. In the heads of the valleys the level of escape and consequently of the water table in the adjacent inter-dike compartments is high. Sear the coast it is low. In the head of vVaikolu Valley, springs occur at altitudes up to ] ,300 feet, and in the inter-dike compartments farther south the water level is probably still higher. Other springs occur along vVaikolu Stream and low on the ·walls of the canyon to an altitude of 500 feet ( pl. 1). The total discharge of these springs, during dry weather, constitutes the entire flow of the stream at the gagiug station, and averages approximately 4.7 million gallons a daJ· (sep table, page 77). Half a mile south of tlw mouth of the stream a series of springs issues on the eastern wall of the canyon at 400 to 500 feet altitude. One of these serves as a source of water forKalaupapa and Kalawao. On June 11, 1935, its discharge was estimated by H. T. Stearns to be about 250,000 gallons daily. It is possible that this group of springs is perched by an ash bed. However, no ash bed could bi~ found, and it is believed more probable that the water escapes from inter-dike compartments at and near the upper edge of the rela tively impermeable alludum banked against the valley side. In the head of Pelekunu Stream springs issue at least as high as 2,000 feet altitude, and probably higher. Only a few of them are shown on plate 1. The lo,v-stage flow of Pelekunu Stream is prob ably largely or entirely from these springs. The average minimum discharge of Pelekunu Stream and Lanipuni Stream (the largP eastern tributary which joins Pelekunu Stream at about H40 fee1 altitude), is about 2.4 million gallons daily (see table, page 77). During tlw same period, tile average minimum flow of Lanipuni Stream was ahm 2.4 million gallons daily, probably largely or en tirely the discharge of springs from inter-dike compartments in the headwate1·s of that stream. Springs from inter-dike compartments in the upper part of Pilipililau Yalley yield about 0.5 million gallons daily. Along the eastern sh01·e of Pelekunu Bay springs issne from inter-dik(> compartments practically at sea level. In the head of ,vailau Valley springs issue from inter-dike com partments up to 2,100 feet altitude, and possibly higher. A small spring at that altitude on the trail to l\Iapulehu issues from allu dum1 but undoubtedly derives its water from inter-dike compart ments behind the thin alhwial cover. Most of the low-stage flow of hoth major branches of ,vailau Valley is diseharge from dike-com- FEET ~~~J A A: 3000 4000 PELEKUNU VALLEY 4000 100 3000 tooo 2000 100 1000 0 "'l c,:i •100 -1000 •200 -2000 8 11 MILES

Figure 16. Section across East Mololmi, showing ground-water conditions. 'l'he vosition of the seetion is shown in figure 15. WATER RESOURCES 77 plex springs. From 1919 to 194:2, the ayerage minimum discharge of Pulena Stream w::is- 4.4, and of "\Vaiakeakua Stream (includin~ Waiokeela Stream) was 2.1 million gallons daily. Other springs issue from inter-dike compartments north of the gaging stations, in the walls of the main valley and in tributaries.

Minimum daily discharge of windward streams, East :Molokai ( in million gallons) a

Pelekunu Valley Wailau Valley Fiscal Waikolu yearb Stream Pelekunu Lanipuni Pulena "\Vaiakeakua Total Stream Stream Stream Stream rnrn-rn:!:o 3.8 1.8 2.0 3.0 1.3 11.9 1920-1921 2.4 1.8 1.9 3.0 1.6 10.7 1!)21-1922 2.8 2.2 1.9 5.0 2.1 14.0 1922-1923 4.7 2.6 2.6 5.0 2.2 17.1 1923-1924 5.3 2.3 3.0 3.8 2.2 16.6 19~4-1925 4.1 2.2 2.6 5.0 1.9 15.8 1925-1926 3.2 2.0 2.2 4.7 1.5 13.6 1926-1927 3.4 1.9 1.8 3:0 1.8 11.9 1927-1928 3.8 2.0 3.3 ... 2.6 . ... 1928-1929 3.2 ... 2.6 6.8 1.7 . ... 1929-1930 ...... 19R0-1fl31 4.8 ...... 1931-1932 6.1 ...... c1937-1938 7.7 3.3 3.6 4.6 3.2 22.4 1938-1939 7.2 3.1 1.7 5.4 2.0 19.4 1939-1940 6.1 3.0 2.6 5.0 2.6 19.3 1940-1941 5.8 2.9 2.2 3.4 2.2 16.5 1941-1942 6.3 2.5 2.3 3.4 1.9 16.4

·=~=!'>= 4.7 2.4 2.4 , 4.4 2.1 15.8

a Data from U. S. Geol. Survey, Water Supply Papers 516, 535, 555, 575, 595, 615, 635, 655, 675, 695, 710, 725, 740, 755, 865, 885, 905, 935, 965. b July of one year to June of the succeeding year. c No records from July 1932 to June 1937.

QUALITY OF GROUND WATER Only two chemical analyses of ground water from the island of Molokai are available. They are listed in the following table, col umns 1 and 2. For comparison there is given in column 3 an analysis of sea water in the adjacent channel between Molokai and Oahu. The water of drilled well 1 (<'olnmn 2 of the table) contains about one-seventh as much chloride as does the sea water. In con trast, the amounts of sodium are approximately one-half, sulfate two-thirds, magnesium twice, and calcium five times the amounts in the sea water, respectively. Obviously, these radicles in the water of drilled well 1 cannot be solely the result of mixing of pure fresh water with sea water. In part, they have probably been derived by solution from the enclosing rocks. The high temperature of the 78 MOLOKAI

water in that well (page 61) suggests, however, heating of the gl'ound water by rising volcanic volatiles, and some of the dissolved material has probably been brought upward with the volatiles. The sulfate is probably of magmatic origin. Most of the soda, magnesia, and lime were probably leached from the rocks traversed by the rising hot gases and solutions. It has been shown that these oxides are readily leached from the basaltic rocks at Kilauea Volcano, on the island of Hawaii, by similar weakly acid solutions arising fron1 the admixture of volcanic gases and ground water.44 The composition of the water from dug well 30, at Kawela, shown in column 1 of the table, appears to be normal for Hawaiian ground water, as shown by comparison with analyses of ,vell water from Oahu.4 :; Much of the surface and ground water on East Molokai is weakly acid, resulting in a high rate of corrosion of steel pipes. The acid is

Chemical analyses of water (in parts per million)

1 2 3

Silica ( Si02 ) ••..••.....•.•..•. 25.4 8. Alumina (Al20a) ...... 3.17 Iron oxide (Fe20a l ...... 0.43 1 l.~ Calcium (Ca ) ...... 11.0 3n::. 427. Magnesium (Mg) ...... 6.!l :rn5. HiR. Sodium (Na) or l Sodium nncl Potnssi11rn. . . ~ 8.3 ~20. 12.53:-.. (Na+K) J Chloride (Cl) ...... Hi.O 2.SDO. Nitrate (NO:d ...... 0.14 t 20.713. Carbonate ( CO;i) ...... :'\one Bicarbonate (HCO:~) ...... H. Sulfate (S04 ) •••.••...•••.• · • • G.U 244. 2,852. lfluoride (F) ...... 0.1 'l'otal hardness ...... 00.1 2.(102. 4.BM. Total solids ...... 119. 37,700. Loss on ignition ...... 36. 7~. pH ...... 6.0 Date ur eulleetion ...... XOY. 15. llJ,lb Dec. H, UH5 Dec. 3:1. Ul2D l. Dug- ,Yell 30 ( Kamakana well). Molokai. Analyst. R. H. 'l'animoto, Board of Health. Territory of Hawaii. 2. Drilled ,vell 1, West Molokai. Anal;yst, A. B..Joy. Pacific Chemical and Fertilizn· Co. 3. Padfic Oeean midway between ?llolokai and Oahu. Aualyst. Dparboru Chemieai Co. Stearns, H. 'l'., and Vaksvik, K. N., Hawaii DiY. Hydrogra1ihy Bull. 1, p. 361, 1935.

" Macdonald, G. A., Solfataric alteration of rocks at Kilauea Yolcano: Am. Jonr. Sci., vol. 242, pp. 496-505, 1944. •s Stearns, H. T., and Vaksvik, K. K., Geology and ground-water r('sources of the island of Oahu, Hawaii: Hawaii Div. Hydrography, Bull. 1. pp. 361-364, 1935. ,YATER RESOURCES 79 largely humic acid derived from the summit swamps. The followin~: list of acidity determinations was supplied b;Y Molokai Ranch, Ltd. ,vater from dug well 30, at Kawela, has a pH of (i.0.

ACIDITY OF 'l'UNXEL AKD S'I'REAi\I WATER Source of Date of ,vater pH sampling Tunnel 8 ...... 6.2 ...... Sept. 17, 1937 Tunnel 9 ...... 6.2 ...... Do. Kawela Stream ...... 6.8 ...... Sept. 14, 1937 Kamoku Stream ...... 5.2 ...... Do. Kalihi Stream ...... 6.4 ...... Sept. 17, 1937 Ohialele Stream ...... 5.6 ...... Sept. 14, 1937

USE OF WATER FROM THE LARGE WINDWARD VALLEYS J>uring the past half-century, several proposals have been made to bring the abundant water of the large windward Yalleys of East Molokai to the dry leeward slopes and the Hoolehua Plain. On the Hoolehua Plain, in particular, large areas of rich soil exist but lack sufficient irrigation water for most agricultural uses. It has been estimated that if the water available in the windward valleys could he brought to the Hoolehua Plain, it would be sufficient to irrigate i"i,000 to 12,000 acres, depending on the type of crops. Several projects have been adYanced for tunneling through the intervening ridgeH and leading the water of the windward streams to the agri cultural areas. Although earlier suggestions of a general nature appear to haYe ht>en made, the first we11-supported plan of this sort seems to have 4 been that by Lindgren. G He presented three alternate suggestions. (1) C'tilization of ,vailau ,vater alone, by means of a tunnel 12,800 feet long which would tap Pulena Stream at (>70 feet altitude, and discharge in l\iapulehu Gulch at 660 feet altitude. (2) Utilization of hoth ,vailau and Pelekunu water, by means of a tunnel 14,500 ft>et long which would tap Pelekunu Stream at 700 feet altitude, and lead the water to Pulena Stream in vVailau Valley, and thence to .Mapulehu Gulch. (3) Utilization of both ,vailau and Pelekunu water, by means of a tunnel 15,000 feet long tapping Pulena Stream at (ii"iO feet altitude and leading the "rater to Pelekunu Stream at HHi"i feet altitude, and thence by means of a tunnel 26,500 feet long to a point at (HO feet altit.ude 1.2 miles east of Kawela Gulch. The positions of the tunnels are shown in figure 17. The water would

• 6 Lindgren, \Y., The water resources of Molokai, Hawaiian Islands: U. S. Geo!. Survey, Water Supply Paper 77, pp. 55-56, 1903; also unpublished report to American Sugar Cp., HJOO. 80 MOLOKAI have been carried from the tunnels to the agricultural areas on Hoolehua Plain, at 450 feet altitude, by a series of ditches, flumes, and siphons. It was estimated that the use of Wailau Stream alone would make available about 8 million gallons of water a day, and Pelekunu and Wailau together would supply about 14 million gal lons. It was expected that the tunnels would also develop large amounts of ground water. The tunnel projects were considered too costly by Lindgren, who recommended instead the development of ground water along the southern coast, and pumping to the agri cultural areas. In 1919, Frederick Ohrt recommended a series of tunnels 18,(;40 feet long to divert water from ·vvaikolu Stream at 580 feet altitude and to deliver it to a point on the cliff aboYe the reservoirs at Kalau papa, for use as domestic water and to generate electric ·power. He suggested that if the construction of a tunnel system along the north coast to supply water to the Hoolehua Plain should in the future prove feasible, these tunnels could be incorporated as part of the large system.47 H. A. R. Austin, in 1929, recommended adoption of Ohrt's proposals, and indicated the belief that it would eventually prove feasible to construct a series of tunnels along the north coast

Kaunakakai

o 3 miles

EXPLANATION >---Main tunnel line proposed by H. Howell >--== Main tunnel line proposed by H.A.R. Austin >-·-·-Alternate tunnel line proposed by H. Howe! I >---- Future tunnel line proposed by HA.R Austin >------Future tunnel line proposed b)' H. Howell =-~= Devslopment tunnel proposed by HAR Austin ----Development tunnel proposed by H. Howell >-········Tunnsl Imes proposed by W. Lindgren Figure 17. Map of East Molokai, showing proposed routes of tunnels to lead water from the wet windward valleys to·the dry leeward slopes.

47 Ohrt, Frederick, Unpublished report to the Superintendent of Public Works, Ter ritory of Hawaii, 1010. WATER RESOURCES 81 to deliver water of the windward streams to the Hoolehua Plain at an altitude of 450 to 500 feet. 48 In 1923, J. Jorgensen proposed the construction of a series of tunnels along the north coast to deliver the water of Wailau, Pele kunu, and ,vaikolu Streams to the Hoolehua Plain at an altitude of 500 feet.49 He estimated that the three streams would yield an average flow of ab~ut 55 million gallons daily, but in order to utilize high-stage discharges in excess of 55 million gallpns, he proposed that the tunnels have a capacity of 100 million gallons daily, the excess to be stored in reservoirs in the Hoolehua area. He suggested that sufficient water for irrigation and power development could be diverted to Kalaupapa. Howell doubts whether the proposed storage capacity, or the capacity of the tunnel during freshet stages, would be sufficient to provide water throug'l10ut some of the longer drought periods.t> 0 In the summer of 1935 H. T. Stearns investigated the geologic structure and hydrologic conditions in the wind·ward valleys in anticipation of the Bureau of Reclamation survey, and proposed to Mr. Hugh Howell that ,vater-development tunnels utilizing the new principal of storing water in the dike complexes be used to make up the deficit in surface run-off during dry periods. In December, 1935, the U. S. Bureau of Reclamation commenced an investigation, under the supervision of Hugh Howell, into the location and amount of suitable agricultural land, the location and amount of available water for irrigation, and methods for delivering this water to the land. Howell's report outlines a program for the construction of tunnels to lead water from ,vailau, Pelekunu, ,vaikolu, and other minor streams, to the Hoolehua Plain, and to supplement the low-stage flow of the streams with water from development tunnels driven into the dike complex in the head:-; of the big valleys.t>1 The proposed locations of the transportation and development tunnels are shown in figure 17. The transportation tunnel would start at the east at vVailau Stream, with a possible future extension to Papalaua Stream. From ,vailau Valley, the tunnel would penetrate the ridge just north of Olokui Peak to Pelekunu Valley, extend thence to the head of Haupu Valley, to ,vaikolu Valley, and to the head of vVaileia Valley.

•s Austin, H. A. R., Unpublished report to the Superintendent of Publie Works, Ter ritory of Hawaii, 1929. <9 Jorgensen, J., Unpublished report on utilization of streams of the windward coast of East Molokai for irrigation of the Hoolehua homesteads, 1923. 50 Howell, Hugh, Final report on water supply studies, Hawaii, F. P. No. 45, Island of Molokai (abridged) : U. S. Bureau of Reclamation, p. 10, 1938. 51 Howell, H., op. cit., G2 pp.; also mimeographed report, unabridged, 111 pp., 1038. 82 ~IOLOKAI

Thence westward two alternative routes were proposed. The pre ferred route would strike almost directly westward, collecting water from vVaihanau Yalley, and emerging at a point about 0.3 mile south of Kualapuu village. The alternate route would strike north \\'estward to ,vaihanau Yalley, and thence extend along the northern coast just inland of the great coastal cliffs, debouching about 2 miles northwest of Kualapuu. The capacity of the tunnel woulcl increase from :rn million galloi:!s daily at the eastern end to 80 million gallons daily west of ,vaikolu Yalley. The total length of the tunnels, fol lowing the p1·eferred route, would be 18.3 miles: and total cost of the project was estimated at 5 million dollars. It was proposed to (leliver to the agricultural areas a minimum of 55 million gallons of \\'ater daily, for the irrigation of about 12,000 acres of land. It was belie,·ed that during most of the time the streams would supply ;,::, million gallons daily or more. Additional ground water or 11nknown amount would be developed by the transportation tunnels cTossing the dike complex. During periods when the stream dis charge is less than 55 million gallons daily, it was proposed to make up the deficit to 33 million gallons from the discharge of water develupmeut tunnels driYen into the dike complex at the heads of the big valleys. :Xine such tunnels were proposed, ranging from 1.0 to 1.9 miles long. The positions of the proposed development tunnels are shown on figure 17. Based on the results obtained at the vYaia hole tunnel system on Oahu, H. T. Stearns concluded that if the tunnels were allowed to flow com;tantly, each could be 1·elied on fo1· :t minimum flo,v of 1 to 3 million gallons daily, but if the tunneh; were plugged and drawn upon only for short periods a considerably greater yield could be expected/'2 Thus, although several possihl(:' sites for the reservoirs in the Hoolehua area were indicated, it was proposed that the principal storage would be underground, in the

'·2 Stearns, II. T., Preliminary report on ground water in ,vailau, Pelekunu and Waikolu: in Howell, H., ov. cit., pp. 21-22. 3 '' Austin, II. A. R., l'.npublished report to Molokai Water Board, on investigation>< rdutivc to the proposed :Molokai ,Ynter Project, Jan. 31. 1944. WATER RESOURCES 83

that valley...Water was to be delivered to the Hoolehua area at the W50 foot level, instead of at 750 feet as proposed by Howell, because it ,vas believed that the corresponding lowering of the intakes would make available about 20 percent more stream water. The main tunnel would have a capacity of 35 million gallons daily at its eastern end, increasing by stages to 72 million gallons daily at its western enu. The minimum amount,of water delivered by the tunnel would be :~3 million gallons daily, as compared to a minimum of 55 million gallons daily as proposed by Howell, because it was believed that an attempt to maintain the higher minimum would necessitate draft from the development tunnels in the dike complex over too great a proportion of the time, resulting in drainage of the inter-dike com partments. To maintain a minimum daily discharge of 35 million gallons three water development tunnels were proposed, each about 5,000 feet long, penetrating the dike complex. Two would be situated at 800 feet altitude in the head of Wailau Valley, and one at slightly higher altitude in Pelekunu Valley. Their proposed locations are shown in figure 17. The tunnels would be bulkheaded to conserve water in the inter-dike compartments, and it was esti mated that the deficiency in stream flow could be made up by an average total draft on the development tunnels of 10.8 million gallons daily for an average of 17 days per month during the 6 months of low stream flow, May to October, of a normal year. During the rest of the year draft on the development tunnels would generally be unnecessary, and a minimum delivery of 40 million gallons daily could probably be safely supplied. Additional develop ment tunnels could be constructed later if so desired. Also, the draft on the tunnels could be increased after a few years if per formance warrants it. The large amounts of ground water encoun tered in digging the transportation tunnels would rapidly uecrease, owing to drainage of the inter-dike compartments, and it was be lieved that eventually the water developed by these tunnels would probably be only about enough to compensate losses from the tunnels. Storage of 100 million gallons would be vrovided in reservoirs in the Hoolehua area, waterproofed by mixing soil and cement and tamping with sheep's-foot rollers. It is believed that the plan would make possible irrigation of 6,816 acres of land. The estimated total cost of the project, including reservoirs, distribution system, and administration, was $6,185,000. It was suggested that water could be delivered from the tunnel to Kalaupapa, eliminating the need of the present pipeline to 84 MOLOKAI

Waikolu Valley. It was also suggested that at a later date tunnels could be constructed from Wailau Valley to intercept the water of Papalaua and Halawa streams, the water being delivered to "\Vailau Valley at about 2,000 feet altitude and dropped to about 750 feet altitude for the generation of electric power. Shortly afterward, in a supplementary report,54 Austin outlined a lower-cost project, involving construction of only the portion of the main transportation tunnel from Waikolu Valley westward, and one development tunnel. The main tunnel would be 52,900 feet long. The development tunnel woll'ld extend 2,000 feet eastward into the ridge between Waikolu and Pelekunu Valleys, and thence 5,000 feet southward across the trend of the dike complex. It was estimated that this system would deliver about 5 million gallons of water daily to the Hoolehua area, at a total cost of $2,815,000 for the project. This tunnel would be more than half as long as that proposed in the preceding project, but would deliver only about one-seventh as much water. Thus, although the total cost of the project would be much less, the actual cost per gallon of water delivered wou1d be much greater.

FUTURE DEVELOPMENTS A large amount of ground water remains to be developed in the island of Molokai. However, the area in which ground water can be developed, and particularly the areas in which specific types of development are possible, are decidedly limited. Figure 15 shows the areas of the island underlain by the several types of ground water. The basal water beneath all, or nearly all, of West Molokai is brackish. No perched water is present. Fresh water confined be tween dikes may possibly occur in a small area in the vicinity of Puu Nana, but the likelihood is not great. Brackish basal water also underlies the Hoolehua Plain. There appear to be no prospects of developing fresh water anywhere west of Kualapuu hill. Likewise, wells on the Kalaupapa Peninsula would yield brackish or salt water. In East Molokai the small amounts of perched water which are present are already largely developed. The spring area along .the upper part of the South Fork of Kaunakakai Gn1<>h is not utilized, but the dry-weather discharge of the springs is so small and the area so difficult of access to a pipeline, that development would probably not be economically feasible. Tunneling there would prob-

114 Austin, H. A. R., Letter to Frank West, Chairman, Hawaiian Homes Commission, Feb. 11, 1944. WATER RESOURCES 85 ably increase the discharge little or not at all. Likewise, further tunneling in the area east and northeast of Kalae would probably not appreciably increase the amount of perched water discharged. Tunnels along buried ash beds in the upper memhPr of the East Molokai volcanic series, in the area west of Waikolu Valley and south of Waileia and Waihanau Valleys, would probably develop some perched water, but the amount would probably be too smalJ to justify the expense of tunneling. Tunnels at Haleloulu Spring, 0.9 mile southwest of Puu Kolekole, at Kahananui Spring, and Ahaino Spring probably would develop little additional water. No economically important bodies of perched water are known in th<' area east of Wailau Valley. A large portion of East Molokai is underlain by fresh basal water ( fig. 15). Anywhere within that area the development of basal wells is limited only by the depth of the waler table beneath the surface, that is, by the economic limit of the depth of the well and the amount of pumping lift. The basal water would probably nowhere be encountered more than a few feet above sea level. Close to the southern coast the basal water is brackish, but short distances inland large amounts of fresh water are available to wells. Maui type wells off er the least danger of becoming salty. In drilling wells, care should be exercised not to drill too far below the water table, particularly where the height of the basal water table above sea level is small. It would be wise to obtain competent geologic advise on specific projected sites before undertaking any large develop ments. Large amounts of fresh water, at altitudes from sea level to more than 2,000 feet above sea level, remain nnrltweloped in the dike com plex of East Molokai. The possibility of development tunnels pene trating the inter-dike compartments in the heads of the big wind ward valleys has already been treated. Similar tunnels driven into the dike complex from the heads of Mapulehu, Kamalo, or Kawela Gulches, or other localities on the southern slope, would develop large amounts of water. However, to insure sufficient head of water in the inter-dike compartments above tunnel level, the tun nels should not be higher than about 1,000 feet altitude. Such a. tunnel started at 1,000 feet altitude in Mapulehu Gulch would enter the dike complex within half a mile, but tunnels started at 1,000 feet altitude in Kamalo or Kawela Gulches would probably extend more than 2 miles before reaching the dike complex. H. A. R. Austin has suggested a development tunnel, at 2,500 feet altitude at a location near Kamiloloa Spring, extending toward Waikolu Valley and under. Kaulahuki hill, which he believed might encounter 86 MOLOKAI dikes.55 The tunnel would, however, probably be at too high an alti tude to develop much water from the inter-dike compartments. It should be borne in mind that any tunnel developing water in the dike complex is removing water from storage. If the water is removed faster than it is replaced by recharge, the storage will be depleted, and the level of water in the inter-dike compartments eventually will be lowered to the level of the tunnel, at which lime the daily yield of the tunnel will be greatly decreased. For that reason, tunnels in the dike complex should be plugged by means of one or more bulkheads at impermeable dikes, fitted with valves, and allowed to flow only when the water is actually needed. A study of pressure gages installed in the bulkheads will inoi<'afa:~ whether, and at approximately what rate, the level of stored water in the inter-dike compartments behind the bulkheads is being lowered. vVhenever pressures indicate that the head of stored water is being lowered too much, the rate of flow from the tunnel should be re duced. In that way water can be conserved in the dike complex for use in time of need.5 6 The need of large amounts of water for irrigation on the Hoolehua Plain has long been recognized. Large amounts of water are avail able, but there is no cheap way of delivering it to the area where it is needed. The possible sources of water are the large windward valleys, or a series of wells on the southern slope of East Molokai. The necessary large amounts of water could be obtained by Maui type wells along the i;:011tlrnrn slope east of Kawela, but delivery to the Hoolehua agricultural areas would entail expensive pipe lines and the cost of pumping. The better solution appears to be the con struction of a series of tunnels, such as those proposed by Howell and Austin, to bring the water in from the wind·ward valleys. (s~ pages 81-84) . Another possibility is the construction of a pipe line to carrJ· water from an intake at about 1,000 feet altitude on vVaikolu Stream, around by way of the coast to Hoolehua. The pipe could be laid along a narrow bench excavated in the windward cliff, crossing Waileia and Waihanau Valleys with siphons. An intak(~ at 1,000 feet altitude on vVaikolu Stream would impound most of the low-stage flow of the stream, or probably never less than 2 million gallons daily. This could, if desired, be augmented by a development tunnel in the head of the valley. It should be possible

55 Austin, H. A. R., Unpublished letter to Frank West, Chairman, Hawaiian Homes Commission, Feb. 11, 1944. 56 Stearns, H. T., and Vaksvik, K. N., Geology and ground-water resources of the island of Oahu, Hawaii: Hawaii Div. Hydrography, Bull. 1, p. 435, 1935. "\V ATER RESOURCES 87 by this means to deliver 2 million gallons of water daily to thp Hoolehua Plain at an altitude of 650 feet, through a 12-inch pipe line approximately 12 miles long. Water from the wind,vard valleys could be delivered to the south ern slope for irrigation by means of tunnels such as those suggested by Lindgren. The shortest route would be that from Wailau Valley to Mapulehu Gulch. Water from such a tunnel at :Mapulehu Gulch could be brought out along the eastern wall of the valley to a point at about 650 feet altitude near the end of the spur, then dropped several hundred feet for the generation of electricity. PAGE 88

(BLANK) PETROGRAPHY OF MOLOKAI BY

GORDON A. MACDONALD

ABSTRACT The lower member of the East Molokai volcanic series consists predomi nantly of olivine basalt, with smaller amounts of basalt and picrite-basalt. In the lower part of the section the picrite-basalts are of the primitive type, <>ontaining numerous large phenocrysts of olivine. In the upper part of the section appear picrite-basalts containing many large phenocrysts of augite as well as olivine. The upper member consists principally of oligoclase andesite, with minor amounts of andesine andesite and trachyte. A <'hemi<'al analysis of a typical oligoclase andesite is given. In and near the caldera complex many of the lavas were partly chloritized, and amygdules and nodules of calcite and quartz were deposited, probably by rising igneous volatiles. In the same area the lavas are intruded by small masses of olivine gabbro. The lavas of the West Molokai volcanic series are olivine basalts, picrite basalts of the primitivP typP, anil ha!'mlts. 'l'he latter are considerably more abundant than in other Hawaiian volcauoes. A few basalts contain a small amount of hypersthene. Following a long period of erosion on East Molokai Volcano, an eruption of mafic olivine basalt built the Kalaupapa Peninsula at the foot of the great northern cliff ; at about the same time an eruption of similar magma off the easti:>rn coast of Molokai built the Mokuhooniki tuff cone. At West Molokai Volcano, the parent olivine basalt underwent only minor differentiation. But in East Molokai Volcano it was differentiated toward . the end of the eruptive cycle into augite-rich picrite-basalts, andesites, and trachytes. The suite as a whole is typical of mid-oceanic volcanoes.

INTRODUCTION The petrographic study is based largely on the examination in thin section of 121 specimens, from localities scattered over the entire island, supplemented by field studies and the laboratory examination of hand specimens. The svecirnens were collected by H. T. Stearns, D. J. Cederstrom, and the writer, during the course of geological and ground-water investigations of the island. A chemical analysis of a specimen of oligoclase andesite was made by Sadamoto Iwashita, in the laboratories of the University of Hawaii.

89 90 MOLOKAI

The compositions of feldspars were determined largely b:v immer sion methods, but partly by extinction angles. Optic a.A.ial auglei,, were estimated from the appearance of optic axis or acute bisectrix interference figures. Rocks in which the average feldspar is labradorite are classed as basaltic; those in which it is andesine or oligoclase as andesites; and those in which it is albite, as trachytcs. The andcsitcs are divided into andesine andesites and oligoclase andesites, depending on the composition of the average feldspar. Basaltic rocks in which olivine forms less than 5 percent are classed as basalts. Those in which olivine forms 5 percent or more, and feldspar 30 percent or more, are classed as olivine basalts. Those (essentially holocrysta1- line) rocks in which feldspar comprises less than 30 percent are classed as picrite-basalts.

PREVIOUS INVESTIGATIONS The earliest, and only other extensive investigation of the petrog raphy of Molokai is that by Mohle,1 who studied about 50 specimens of lava and several of tuff collected by Schauinsland. Although Mohle states that the localities were scattered over the entire island, most of the specimens came from the great northern cliff of East Molokai or its immediate vicinity. The lavas were divided into three groups. Those of the first group were described as normal olivine bearing basalts, characterized by large feldspar phenocrysts. Their olivine content was not large, but moderately uniform. All but one came from the cliff behind Kalaupapa Peninsula. The rocks of the second group were reddish-brown lavas in which olivine was nearly or totally absent. They were believed to represent flow crusts. In the third group pyroxene was said to be present in only small amount, or absent altogether, its place being taken by abundant olivine. One contained irregular flakes of biotite. The first two of these groups may correspond with the olivine basalts and basalt8 of the present paper, but the writer has found no rocks which corre spond to l\fohle's description of those of his third group, either on Molokai, or on any other of the Hawaiian Islands. A dense dark basalt from Kalae was described by Mohle as containing a few four and six-sided cross-sections of nepheline, and was <;:lassed as "neplw line basanitoid." No rock of this sort has been found on Molokai during the present investigation, and either the locality or the determination of nepheline must be regarded as erroneous. A small "bomb,'' about the size of a hen's egg, was reported to consist of

1 Mohle, F., Beitrag zur Petrographie der Sandwich- und Samoa- Inseln : Neues Jahrb., Beil. Bd. 15, pp. 71-82, 1902. PETROGRAPHY 91 orthorhombic pyroxene, olivine, monoclinic pyroxene, and picotiie, and was compared to similar bombs from Oahu. No rock of this sort has been found during the present study. It is possible that both these specimens were mislabeled, and actually came from the late volcanics (Honolulu volcanic series) on Oahu. A specimen of olivine gabbro was not unlike some of those described in the present report. Lindgren2 paid little attention to the lavas of Molokai, describing them briefly as principally normal "feldspar basalt," containing olivine, and in part also phenocrysts of soda-lime feldspar. From the west fork of Wailau Valley he described boulders of a coarse grai11eu iulrusive rock, termed by him olivine diabase, composed of calcic plagioclase, augite, olivine and magnetite. The rock is un doubtedly the same as that described on a later page of this report as olivine gabbro. Cross3 reviewed the work of both :Mohle and Lindgren, but added no new descriptions. Powers4 recorded the presence of basalt with abundant olivine, "feldspar basalt" with conspicuous phenocrysts of plagioclase, and nonporphyritic olivine-free basalt at West Molokai Volcano. East Molokai Volcano he believed to consist "largely of feldspar basalt with rare alkali trachyte". He compared the lavas to those of Kohala Volcano on Hawaii. He described a basaltic rock, contain ing feldspar phenocrysts "sometimes one or two inches long and 1/4 inch thick," larger than any observed by the writer. The lava form ing the Kalaupapa Peninsula was recognized as olivine basalt.

2 Lindgren, W., The water resources of Molokai, Hawaiian Islands: U. S. Geol. Sur· vey, Water-Supply Paper 77, pp. 14-15, 1903. s Cross, W., Lavas of Hawaii and their relations: U. S. Geol. Survey, Prof. Paper 88, pp. 24-25, 1915. • Powers, S., Notes on Hawaiian petrology: Am. Jour. Sci., 4th ser., vol. 50, pp. 259, 269, 271, 1920. 92 MOLOKAI

TERTIARY VOLCANIC ROCKS

EAST MOLOKAI VOLCANIC SERIES LOWER MEMBER GE~ERAL CHARACTERISTICS.-The lower member of the East l\folo kai volcanic series comprises the great mass of little-difterentiated basaltic lavas which built the primitive shield volcano. By far the most abundant type of rock is olivine basalt, but there also occur flows of basalt containing little or no olivine, and others of picrite basalt containing very abundant phenocrysts of olivine or olivine and augite. The flows are both aa and pahoehoe in type. Locally, there are found between the flows thin beds of vitric ash and ashy soil. The lavas of the caldera complex are of the same type as those outside the caldera, and originally differed from them only in greater massiveness and thickness owing to ponding. Within the area of the former caldera, however, the lavas are characterized by a large amount of secondary mineralization, presumably the result of the rise of abundant volatiles in the volcanic focus. Nor mally, on the outer slopes of the volcano the lavas are not amygda loidal, even a thin layer of calcite in the vesicles being rare, but in the caldera area amygdules and vesicle linings are very common. The commonest secondary mineral is calcite, but quartz and chalce dony are nearly as abundant. In addition to vesicle linings and amygdules, quartz and chalcedony occur as irregular nodules, up to 6 inches or more across. Accompanying the deposition of second ary quartz and calcite, many of the lavas were partly chloritized, the chlorite being derived partly from ferromagnesian minerals and partly from interstitial glass. Similar hydrothermal alteration and secondary mineralization are found in the Kailua area on Oahu, which is interpreted as the ancient caldera of the Koolau Volcano,5 and less cunsvicuuusly in the caldera area of the Waianae Volcano on Oahu. The general character of the lower member of the East Molokai volcanic series is well shown in the following stratigraphic section, measured along the trail which leads from Kalae down the great northern cliff to the Kalaupapa leper settlement (plate 1).

5 Stearns, H. T., and Vaksvik, K. N., Geology and ground-water resources of the island of. Oahu, Hawaii: Hawaii Div. Hydrog., Bull. 1, pp. 88-90, 1935; Stearns, H. T., Supplement to geology and ground-water resources of the island of Oahu, Hawaii: Hawaii Div. Hydrog., Bull. 5, pp. 48-50, 1940. PETROGRAPHY 93

Stratigraphic section of East Molokai volcanic series along the trail from Kalae to Kalaupapa Thickness (feet) Andesite aa, dense and nonporphyritic...... 16 Baked red soil...... 0-¥2 Andesite aa, dense and nonporphyritic...... 57 Andesite aa clinker ...... 8 Andesite aa. nonwrph:vritic ...... 10 Andesite aa clinker ...... 6 Andesite aa. dense and nonporphyritic...... 10 Andesite aa clinker ...... 8 Andesite aa, with a few feldspar phenocrysts up to 2 mm long. . . . 29 Andesite aa clinker ...... 27 .A.ndesite aa, dense and nonporphyritic...... 28

I Red ashy soil ...... 1/4 -1 J Olivine basalt aa clinker, weathered red at top...... 4 I Olivine basalt aa, with moderately abundant olivine phenocrysts up to 5 min long...... 8 Aa clinker ...... 3 Olivine basalt aa, with moderately abundant olivine phenocrysts up to 3 mm long ...... 5 Aa clinker ...... 4 t Olivine basalt aa, with scattered phenocrysts of olivine and feldspar up to 4 min long...... 12 Olivine basalt pahoehoe, with abundant feldspar phenocrysts up to 1 cm long, and a few of olivine and augite up to 5 mm long. Many flow units averaging about 5 feet thick...... 71 Olivine basalt aa, ,vith abundant feldspar phenocrysts up to 5 mm long ...... 26 Aa clinker ...... 12 Olivine basalt aa, with moderately abundant phenocrysts of feldspar, olivine, and augite up to 7 mm long...... 21 ~ Olivine basalt pahoehoe, with moderately abundant phenocrysts of i f~~~inJ0~~~!t~~~~~. ~~ ·t·o· ~ -~~ .1~~1.g.' -~1~~ .~ ~~~ ~~- ~ ~~~~e:. ~~-~~~·~~ 22 ·208, 1931 ; The crystallization process of basalts: Am. Jour.' Sci., C>th ser., vol 81, pp. 824-828, 1936._ · PETROGRAPHY 97 contains almmlaut large crystals of all three of the common pheuo crystic minerals, feldspar, olivine, and augite. The three are gen erally present in nearly equal abundance, and together comprise _as much as 40 or 50 percent of the rock. The abundance of phenocrysts suggests that at the close of eruption of the lower member the basaltic magma of the reservoir had reached a temperature at which it was supersaturated in all the major silicate constituents. The groundmass of the olivine basalts is intergranular or inter sertal, with an average grain size ranging from about 0.03 mm to 0.1 mm. In general, the pahoehoe is intersertal, and the aa is inter granular; and the average granularity of the pahoehoe is some what greater than that of the aa. However, the variation is so great as to make this generalization very tenuous. The principal con stituents of the groundmass are feldspar and monoclinic pyroxene, the latter being generally only a little the less abundant. The feld spar ranges from medium to sodic labradorite. In most specimens the pyroxene is pigeonite, with 2V close to O°, but in a very few it is augite. Olivine occurs in the groundmass of all the olivine basalts. In many it is stained pale brownish-green by slight alteration, and in some it is altered to iddingsite or material closely resembling it. Black opaque oxides form 5 to 15 per cent of the rock. They generally include both magnetite and ilmenite, though in a few rocks magnetite alone .appears to be present. Apatite appears in many specimens as minute highly acicular crystals generally en closed in feldspar. Several specimens contain small :flalrns of biotite, pleochroic from pale straw yellow to deep reddish-brown. The biotite flakes are anhedral, lying between the other constituents, or project into vesicles. They were formed during a very late magmatic or post-magmatic stage. Interstitial glass is present in the rocks ,vith intersertal texture. It is pale brown to <'olorlPRR, t.l1P Mlor generally becoming deeper with an increase in amount. E.xcept in pahoehoe crusts, however, the proportion of glass does not much exceed 5 percenL vYHhin the cahlera complex some rocks contain interstitial chlorite, apparently derived in part from glass, and in part from ferromagnesian constituents of the groundmass. BaSALTs.-The basalts are essentially like the olivine basalts, except that olivine is sparse or entirely absent. Gradations to the olivine basalts occur. A few specimens are nonporphyritic, but most contain scattered to moderately abundant phenocrysts of feldspar. The maximum size of the phenocrysts is less than in the olivine basalts, the greatest length observed being 7 mm. The cores of the phenocrysts are labradorite-bytownite to calcic labradorite; the · thin rims are medium to sodic labradorite. Rarely, a few pheno- 98 MOLOKAI crysts of olivine are present, and these may be partly altered to iddingsite. The groundmass is intergranular or intersertal, com posed of medium to sodic labradorite, monoclinic pyroxene, magne tite, ilmenite, a little apatite, and glass. Olivine is lacking or presem in very small amount. Where its nature has been determined, the pyroxene is pigeonite. "\Vithin the caldera complex many of the rocks have been consicl erably chloritized. In a nonporphyritic basalt collected at 1,230 feet altitude along Pelekunu Stream the ferromagnesian minerals have been almost entirely destroyed, although the feldspar (medium labradorite) appears to have been little affected. There remains only an aggregate uf feldspar, chlorite, iron oxides, and calcite. In a basalt from 1,440 feet altitude in Pulena Stream, a tributary of vVailau Stream, feldspar phenocrysts are altered to an aggregate of calcite, chlorite, and a clay mineral with low birefringence and a refractive index of about 1.54. The groundmass consists of plagio clase, iron oxide, and abundant chlorite. Residuals of fresh feldspar appear to be medium labradorite, but much of it is altered to a more sodic feldspar, apparently oligoclase. PICRITE-BASALTs.-The picrite-basalts also are intergradational with the olivine basalts, differing from them principally in the greater proportion of ferromagnesian minerals. As in other Ha waiian volcanoes,9 two types of picrite-basalt can be recognized. One of these is characterized by the abundance of olivine pheno <..:rysts, either alone or with a few phenocrysts of feldspar or augite. The other contains phenocrysts of both olivine and augite, in roughly equal abundance, with or without a few phenocrysts of feldspar. The first type occurs associated with olivine basalt and basalt in the primitive lava shields of Hawaiian volcanoes, and has been termed the primitive type of picrite-basalt. The second type, termed the augite-rich type of picrite-basalt, appears later in the stratigraphic succession of those volcanoes erupting more highly differentiated lavas. In the lower member of the East Molokai volcanic series, picrite basalts of the primitive type appear lo,v in the section, in the big valleys and in the northern cliff. Olivine phenocrysts reach a length of about 8 mm, and may comprise as much as 50 percent of the rock. They have a 2V close to 90°. Typically they are partly resorhP

9 Macdonald, G. A., Petrography of the island of Hawaii: U. S. Geol. Survey, Prof. Paper, in press. l'lat!' 1-L\. ],Jm,t wall or K,ll!ialo Clulch, from tlw \\'Psi. ;;lwwing thi11-b,•ddPd basalts ol' tlw 1011·<'1' l!H'llllH·r of till· t•:a:-;t ::\lolokai nd(·a11i(· :-;('rip:,: 01·pl'luiu l1y the KHapallu ds(·uns douiP nud thi<·k 1!ow of amlesik. l'huto l1y <: .•\. l\l:w(louald. l'lal!! 1-IB. I•:ast Molukai from Ka111wlrnlrni wharf. slw\\ing its g,•1t(•ral do1tti(·HI prolil<'. ('i1Jdt•1· (·uw•s al,111g till' rift ZollP, tlu• -.;t1•Pp so11thPn1 ;,;lopl', aml tlw alluvinl flats alo11g the (·rni;;r. L'llo!o J1y U. A. l\la1·don11ld. l'late lCIA. Tl1in-t1eddt•d aa alJ(1 Jinlw<•hoe lavas of tlw '\Yest ::\folokai vokanic· st· ri<':-. near Haleua. Small tilled and partly filled 11a h0Pl10e tubes are dearlr Yi,sible. Photo 11:,- C. K. '\Y1•nt worth.

Plate J;iB. Oligo{'lase nrnlt'site pf thP npper llll·llllH·r of the Ea,:;t :::\lolo kai Yoka11ic series. n•,:;tilig: 011 n· sidnal ,:;oil at the top of the basalts of tile lo,yei· mPmlJer. in a roaclcut 0.2 mile uortlwast of '\Yaialua. Photo G..A. ::\lacdonnld. PETROGRAPHY 99

Augite-rich picrite-basalts occur in the upper part of the section. their range overlapping somewhat that of the primitive type (see stratigraphic section, page 93). Olivine phenocrysts resemble in size, composition, and alteration those of the primitive type. Augite phenocrysts reach a length of 1 cm. They have an optic angle of 50° to 60°, and moderate to strong inclined dispersion. Many are zoned, the outer part having a smaller extinction angle and smaller 2V than the core. Augite phenocrysts are generally about equal in abundance, or are slightly more abundant, than those of olivine, and together they constitute 40 to 60 percent of the rock. A few feldspar phenocrysts are present in some specimens, consisting of cores of medium or sodic bytownite enclosed in thin shells of calcic to medium labradorite. Through an increase in the abundance of feldspar phenocrysts these rocks grade into the type of olivine basalt rich in large phenocrysts of feldspar, olivine, and augite, described above. The groundmass is essentially the same as that of the olivine basalts, although in analyzed specimens from Haleakala Volcano, on Maui,10 subtraction of the composition of the pheno crysts and recalculation of the remainder to 100 percent, shows the groundmass to be somewhat more femic than the ordinary olivine basalts.

UPPER MEMBER GENERAL FEATURES.-The lavas of the upper member of the East Molokai volcanic series, which form a thin cap over the East Molokai basaltic shield volcano (pl. 14A), are predominantly oligoclase andesite. In a few specimens, otherwise essentially like the rest, the feldspar is sodic andesine. Trachytes have been identified at only two localities, but at other of the viscous domes in the wet summit area the rocks arc too much weathered for certain identi fication~ It is probable that some of these also are trachytes. The rocks of the upper member of the East Molokai volcanic series closely resemble those of the Honolua volcanic series on West Maui,11 and the Hawi volcanic series of Kohala Volcano on the island of Hawaii.12 OLIGOCLASE ANDESITEs.-The typical oligoclase andesites are me dium to light gray rocks, with moderately to well developed platy jointing parailel to the flow surface (pl. 15B). Platy joint blocks

10 Macdonald, G. A., and Powers, H. A., Contribution to the petrography of Haleakala Volcano, Hawaii: Geol. Soc. America Bull., vol. 57, pp. 115-124, 1946. 11 Macdonald, G. A., Petrography of Maui: Hawaii Div. of Hydrog., Bull. 7, pp. 320-325, 1942. 12 Macdonald, G. A., Petrography of Hawaii: Hawaii Div. of Hydrog., Bull. 9, p. 196, 1946. 100 MOLOKAI

generally exhibit a distinct micaceous-appearing, almost schistose sheen, owing to the parallel arrangement of innumerable small tabu lar feldspar crystals. Rare pahoehoe flow-types occur, but much more abundant are flows of the aa type. In many of the latter, the fragments in the scoriaceous part of the flow are more rhomboid and less clinkery and spinose than in typical aa, and the flows approach the type characteristic of andesite volcanoes, known as block lava.13 Porphyritic and nonporphyritic forms are nearly equally abundant. Of the 43 specimens studied, 19 are nonporphy ritic and 24 porphyritic. The phenocrysts are preponderantly feld spar. Only 4 specimens contain phenocrysts of olivine, and two of these contain feldspar phenocrysts as ,vell. The feldspar phenocrysts range from sparse to moderately abun dant. They are generally 1 to 2 mm long, but rarely attain lengths as great as 8 mm, and one specimen contains a phenocryst of labra dorite-andesine 2 cm long, much rounded by resorption. They show normal zoning, the soda content increasing outward. The core is generally medium andesine, less commonly sodic andesine, and still less commonly calcic andesine. In one specimen, mentioned above, the core is labradorite-andesine, and in one it is sodic labradorite. The outer shell of the phenocrysts is calcic or medium oligoclase, of the same composition as the feldspar of the groundmass. Olivine phenocrysts of megascopic size are generally rare and less than 2 mm in length. However, in one specimen, collected on the ridge 0.2 mile S. 85° ,v. of Pualanalana Bay, olivine phenocrysts reach a length of 3 mm, and form about 5 percent of the rock. They have -2V = 75°, corresponding to a forsterite content of about 35 percent. Although megaphenocrysts of olivine are rare, micro phenocrysts are present in most of the specimens studied. They are geuerally partly, or even entirely, altered to iddingsite. In a few thin sections the iddingsite is surrounded by a thin envelope of fresh olivine, and in many the groundmass olivine is fresh, indicating that the altered microphenocrysts are probably of intratelluric origin. :Magnetite microphenocrysts, up to about 0.7 mm across, are p1·es ent in about hvo-thirds of the specimens. A fe,v specimens contain microphenocrysts, up to about 0.1> mm long, of an acicular amphibole resembling riebeckite, but less strongly colored. This mineral has been found also in the oligoclase andesites of West Maui and Kohala. It has X /\ c small, +2v large, birefringence very low, and distinct pleochroism with X = brown ish-gray and Z = pale brownish-yellow.

1a Finch, R. H., Block lava: Jour. Geology, voL 41, pp. 769-770, 1933. PETROGRAPHY 101

The groundmass of the oligoclase andesites is generally trachytie. The principal constituents are feldspar and monoclinic pyroxene, with smaller amounts of olivine and opaque iron oxides. The feld spar is calcic to medium oligoclase. In some of the rocks some or all of the oligoclase has a small positive optic angle, and is probably potassic.14 The pyroxene is colorless in thin section. In all speci mens in which its properties were determined, it is pigeonite. The olivine is generally fresh, but in some rocks it is stained pale brown ish-green by slight alteration. In most rocks the opaque mineral is largely or entirely magnetite, but in others both magnetite and ilmenite are present. Irregular flakes of hematite occur in some specimens. Fairly commonly, the larger grains of pyroxene exhibit sieve structure, and over small areas small irregular patches of pyroxene scattered amongst grains of the other minerals show common orientation. Numerous minute highly acicular grains of apatite are enclosed in the feldspar. Interstitial colorless glass is present in a few rocks, and _in others there is a little interstitial chlorite. Small grains of the riebeckite-Uke amphibole are present in the groundmass of several specimens. · About half the rocks studied contain a few small flakes of brown biotite. In a specimen collected 0.25 mile southwest of the triangula tion station on Ooa Hill it is unusually abundant, forming flakes up to 0.3 mm long, occupying interstices between the other minerals and projecting into vesicles. It obviously was formed in a very late magmatic or postmagmatic stage. It has ~2V = 20°, r < v strong, .and strong pleochroism with X · pale yellmv to nearly colorless, Z = deep reddish-brown. A few small grains of greenish-brown hornblende are present in the groundmass of an oligoclase andesite flow exposed in an old railroad cut near the eastern edge of Kaluaapuhi Pond, and another at the eastern rim of the gulch 0.6 mile N. 37° ,v. of the nortlnvestern corner of Puhiomu Pond. The latter specimen, and two others, con tain pseudomorphs of finely granular magnetite replacing some prismatic mineral, possibly hornblende or possibly the riebeckite like amphibole. A chemical analysis of a typical specimen of oligoclase andesite is given in column 1 of the accompanying table. The specimen was collected along the highway from Kaunakalrni to the airport, at 380 feet altitude, 0.35 mile N. 19° W. of benchmark 354. The rock is medium gray, dense, and nonporphyritic in hand specimen, with moderately well developed platy jointing, and a micaceous-appear-

H Macdonald, G. A., Potash-oligoclase in Hawaiian lavas: Am. Mineralogist, vol. 27, pp. 793-800, 1942. 102 MOLOKAI

ing sheen on the joint surfaces. In thin section microphenocrysts of feldspar and olivine are seen to grade in size into the ground mass. The olivine crystals are fresh and euhedral. The feldspar phenocrysts consist of cores of sodic andesine, enclosed in thin shells of medium oligoclase. A few grains of magnetite and the riebeckite-like mineral also attain the dimensions of micropheno crysts. The trachytic grournlmass consists uf medium oligoclase, monoclinic pyroxene, olivine, opaque iron oxides, minute needles of apatite, a few flakes of purplish-brown biotite, and a few grains of the riebeckite-like mineral. The iron oxides include both magnetite and ilmenite, with the former predominant. Many of the feldspar phenocrysts show a small optic angle, which appears to be the result of overlapping Carlsbad twin lamellae, as described by Sugi.15 Many grains of the untwinned groundmass oligoclase also show a small positive optic angle, which is believed to indicate a small admixture of potash feldspar. The approximate mineral composition of the rock, estimated by means of traverses with a grilled ocular, is: plagioclase phenocrysts 8%, groundmass feldspar 50%, pyroxene 22%, olivine 5%, iron oxides 12%, apatite 2%, riebeckite-like min eral and biotite 1 o/o.

CHEMICAL ANALYSES OF OLIGOCLASE ANDESITES (1) (2) Norms (1) (2) Si02 ...... 53.14 51.35 Al20::; ...... 14.60 16.34 Q ...... 2.22 Fe20;; ...... 5.74 4.64 or ...... 12.79 11.12 FeO ...... 7.72 6.11) nb 30.30 1.2.11 MgO ················ 2.50 3.73 an ...... 12.51 16.40 CaO ...... 5.44 6.61 di ...... 15.55 8.04 Na 20 ...... 4.64 5.01 hy ...... 3.95 3.96 K 20 ...... 2.20 1.94 ol ...... 3.54 H 20+ ...... 0.38 nit ...... 8.35 6.73 H 20- ...... : ... . 0.22 il ...... 5.17 5.17 Ti02 ...... ~.74 2.74 ap ...... 2.35 2.35 P205 ...... 1.03 1.00 MnO ...... 0.26 0.20 Total ...... 100.61 (1) Oligoclase andesite, upper member of East Molokai volcanic series; on highway from Kaunakakai to Hoolehua airport, at 380 feet altitude. S. Iwashita, analyst. (2) Average oligoclase andesite of the Hawaiian Islands; average of 11 analyses, including one "oligoclase gabbro" (kauaiite). Macdonald, G. A., The Hawaiian petrographic province: in preparation.

Compared to the average analysis of oligoclase andesite of the Hawaiian Islands, shown in column 2 of the table, the Molokai

15 Sugi, K., On the nature of some plagioclase apparently with small optical angle..• , : Kyushu Imp. Univ., Fae. Sci. Mero., ser. D, vol. 1, pp. 1-22, 1940. PETROGRAPHY 103 specimen is a little more silicic, as shown by the presence of quartz and absence of olivine in the norm, slightly richer in potash and iron oxide, and slightly poorer in alumina, magnesia, lime, and soda. A.NDESINE ANDESITEs.-The andesine andesites are essentially iden tical to the oligoclase andesites except for the slightly more calcic nature of the plagioclase. Only four occurrences of this type of rock were found. The dominant feldspar is sodic andesine. All other constituents are the same as those of the oligoclase andesites. The rocks are much more like the oligoclase andesites than the typical andesine andesites of Haleakala Volcano on Maui, or Manna Kea on Hawaii, and are to be regarded as merely the most calcic mem uers of the oligoclase andesite group. TRACHYTEs.-Rocks definitely identified as trachyte have been found only at the viscous dome of Puu Kaeo, on the western rim of Waikolu Valley, and the small cinder cone Puu A.noano, 1.3 miles west-northwest of Kalae. Specimens from some of the other vents in the swampy area near the rims of ,vaikolu and Pelekunu Valleys may be trachyte, but are too weathered for certain identification. The presence of trachyte in the drainage basin of ,vailau Valley is proven by the discovery by Powers16 of a trachyte stream pebble near the mouth of that valley. The trachytes of Puu Kaeo and Puu A.noano are closely similar to those of West Maui. The rock from Puu Kaeo is light gray and dense, with many tabular phenocrysts of feldspar, up to 2 mm long, arranged in a fluidal texture. The rock is considerably weathered. The centers of the feldspar phenocrysts are altered to a fine-grained aggregate of clay minerals, leaving only a thin rim of fairly fresh calcic albite. The trachytes of West Maui contain phenocrysts of calcic to medium oligoclase enclosed in a thin shell of albite,17 and it is probable that the phenocrysts of the trachyte of Puu Kaeo originally had a similar composition. A few small phenocrysts of some former acicular min eral, possibly hornblende, much rouniJP.il and embayed by resorption, are now represented only by pseudomorphs of finely granular mag netite. Microphenocrysts of magnetite up to 0.2 mm across, and a few of olivine and augite, also are present. Those of olivine are partly altered to iddingsite. The groundmass is a very fine grained aggregate of calcic albite, monoclinic pyroxene, magnetite, and de composition products. It is not impossible that the albite was derived from some originally more calcic feldspar, by weathering,

1a Powers, S., op. cit., p. 271. 17 Macdonald, G. A., Petrography of Maui: Hawaii Div. of Hydrog., Bull. 7, p. 324, 1942. 104 .:.\lULUKAl but this seems unlikely as the groundmass feldspar appears to bt> fairly fresh. The trachyte of Puu Anoano is very similar to that of Puu Kaeo, even to the decomposition of the cores of the feldspar phenocrysts. The groundmass appears fairly fresh, and is a little coarser tha11 that of the other rock. The iron oxide is largely magnetite, but a lillle of il avveans tu lJe ilrueuHe. The P.Y ruxeue is vigeouite. INCLUSIONS IN LAVAS.-A few flows of oligoclase andesite contain angular to subangular inclusions of gabbro and dunite, up to about 2 inches across. A flow cropping out a mile northeast of Kapukaulua triangulation station contains inclusions of olivine gabbro, consist ing of medium labradorite (60%), augite (28%), olivine (10%), and iron oxides (2%), arranged in a granitoid texture with an average grain size of about 1.5 mm. The dunite inclusions generalJy consist very largely of anhedral grains of olivine, with a small amount of iron oxide, probably magnetite. One specimen of dunitP contains a few grains of augite.

INTRUSIVE ROCKS Large numbers of dikes cut the lavas of the lower member of the East Molokai volcanic series in the rift zones and the caldera com plex. They show the same variation in composition as the lava flows, of which they were the feeders. Many of them have glassy selvages a quarter of an inch to an inch thick, in which the texture is hyalopilitic. The central parts of the dikes have the same textures as the extrusive rocks. ,vithin the caldera complex there are several small stocks and other intrusive masses of olivine gabbro. 1\1ost of them are dense, but some show locally an open miarolytic structure resembling that of certain gabbros of ,vest Maui.18 The texture is granitoid (hyp idiomorphic granular), and the average grain size ranges from 1 to 3 mm. The rocks consist principally of plagioclase, mouoclinil' pyroxene, and opaque iron oxides. Olivine is present in most speci mens. In a few olivine is absent, but its place is probably taken by chloritc and serpentine alteration products. The plagioclase is gen erally zoned, ranging from sodic bytownite or calcic labradorite to sodic labradorite or in a few specimens calcic andesine. The pyrox ene is augite, with +2v = 55°, and weak to moderate dispersion. In a specimen collected at 1,580 feet altitude in Pulena Stream (a tributary of \Vailau Stream) the augite grades into pigeonitic

1s Macdonald, G. A .. Petrography of Maui: Hawaii Div. of Hydrog., Bull. 7, p. 328, pl. 43C, 1942. PETROGRAPHY 105 augite, with an optic angle of about 4:0°. The iron oxides include l>oth magnetite and ilmenite. A little hematite is present in a few slides. Small apatite grains are enclosed in the feldspar in some specimens, and in one it forms large prismatic grains as much as 2 mm long and 0.2 mm wide. In a few rocks, a small amount of interstitial chlorite is probably derived by alteration of glass.

Several specimens contain scattered grains of reddish-bro,vn biotite7 and in a pebble from the mouth of 1Vailau Stream biotite comprises about 5 percent of the l'Ock. A gabbro cropping out at 870 feet alti tude in Pulena Stream contains a few small grains of bro,vnish ~reen hornblende.

WEST MOLOKAI VOLCANIC SERIES GENERAL FEATUREs.-All of the lavas of "\Vest Molokai Volcano are basaltic. Olivine basalts are probably preuomiuaut iu the lower part of the section, but basalts become very abundant in the upper part. Random sampling over the surface of the shield yielded nearly twice as many samples of basalt as of olivine basalt. The latest lavas, erupted at scattered points over the shield surface, are nearly all olivine basalts, however. A few picrite-basalts of the primitive type occur throughout the section, except among the very latest lavas. Many of the West Molokai lavas are very thin bedded, ranging from less than a foot to two feet in thickness (pl. 15A), and must have been erupted in an exceedingly fluid condition. In the upper part of a section in the face of the fault scarp three-quarters of a mile north of Puu Kana, the lavas are more consistently thin-bedded and poorer in olivine phenocrysts than any other series of flows seen by the writer in the Hawaiian Islands. The latest lavas of West Molokai Volcano were erupted from a few scattered vents, among which are 1Vaiele, Kaeo and Kaa cinder cones, and unlocated vents which produced :flow-remnants cropping out at Kaawa hill, southeast of Kaeo hill, and just southwest of Kahaapilani hill (figure 18). On the lower end of the spur below Kaawa a prominent dike (plate 1) is seen to pass into a :flow. These latest :flows rest on a layer of tuffaceous soil 1 to 3 feet thick, gen Prally baked at the top. All but two of these :flows are olivine basalt; only the specimens collected 0.7 mile S. 74° E. of Kaeo hill and 0.2 mile S. 68° W. of Kahaapilani hill are basalts poor in olivine. OLIVINE BASALTs.-More than half of the specimens of olivine basalt from 1Vest Molokai volcano are nonporphyritic. This abun dance of nonporphyritic rocks is decidedly unusual among the primi• tive lavas of Hawaiian volcanoes. Of the porphyritic specimens, all contain phenocrysts of feldspar, rarely up to 5 mm long but 106 MOLOKAI generally less than 2 mm. Small olivine phenocrysts also are present in most porphyrHic specimens, but in general arc a little less abun dant than those of feldspar. This dearth of olivine phenocrysts does not reflect a similar deficiency in the rock as a whole, for olivine is quite abundant in the groundmass. The feldspar phenocrysts consist of cores of labradorite-bytownite or calcic labradorite, i-mrrounded by thin shells of more sodic plagio clase with the same composition as that of the groundmass. Olivine phenocrysts have an optic angle dose to 90°, are generally partly resorbed, and altered around the edges or even throughout to iddings ite. Both grade in size into the groundmass. l\:'.licrophenocrysts of augite (+2V = 55 °) , grouped together in glomerocrysts, are pres ent in only one specimen collected 0.15 mile inland from the western edge of Pakanaka Fishpond. Magnetite microphenocrysts, up to 0.2 mm across, are found in a few specimP-nR. 157'15' 10'

157"15' 10'

EXPLANATION + + + + + + + + + -t ,.,. I + + + + + Cinder cones Late lava flows Lava flows of of West Molokai West Molokai Figure 18. Map of West Molokai, showing position of late lava flows. PETROGRAPHY 107

The groundmass is intergranular or intersertal. The average grain size generally ranges from 0.01 to 0.07 mm, but some of the latest lavas are unusually coarse grained, averaging 0.1 to as much as 0.4 mm in grain size. These very coarse-grained rocks are non porphyritic. The groundmass (or the entire rock in nonporphyritic specimens) consists of intermediate to sodic labradorite, monoclinic pyroxene, olivine, magnetite, ilmenite, apatite, and interstitial glass. The apatite occurs as minute highly acicular crystals generally enclosed in feldspar. Small flakes of late-formed brown biotite art> present in several specimens. In most rocks the pyroxene is pigeon ite, but in a few, especially those of unusually coarse granularit;r, it is augite (2V = 55°). Some of these rocks, particularly the coarse-grained late lavas, contain an unusually large amount of groundmass olivine. A specimen of nonporphyritic lava from a thin flow in Kahalelani cone contains about lG percent olivine; another collected 0.95 mile S. 42° E. of Puu Nana contains 15 percent; others collected respectively 0.25 mile north of Kaeo hill and 0.75 mile S. 34° E. of Waiele hill contain 20 percent. In some specimens the groundmass olivine is partly or largely altered to iddingsite or a mineral resembling it, probably by ordinary weathering. A non porphyritic olivine basalt from an ancient Hawaiian adz quarry 0.:2 mile northeast of Kaeo hill contains small vesicles which are lined or entirely filled with chlorite. PICRITE-BASALTs.-The picrite-basalts in the West Molokai vol canic series are all of the primitive type, containing abundant phenocrysts of olivine, but none of augite. The olivine phenocrysts range in size up to 8 mm long, and in abundance up to 45 percent of the rock. They are partly resorbed, and altered around the edges to iddingsite. Their optic axial angle is close to 90°. The ground mass is like that of the olivine basalts, already described. A specimen collected 2.65 miles S. 67° w_ of Pohakuloa trig. station eontains in the groundmass irregular patches and streaks of pegmatitoid matter, with an average granularity of 0.15 mm, as compared to 0.03 mm in the rest of the rock. Both augite and pigeonHe are preseut in the pegmatitoid patches, together with the other normal ground mass minerals, whereas in the fine-grained portion of the ground mass all of the pyroxene is pigeonite. In some of the coarse patches the crystals are arranged radially. BASALTS.-The basalts are in general much like the olivine basalts, except for the absence or near-absence of olivine. Roughly a third of the specimens contain no olivine; in the rest it ranges from 1 to 4 percent. Also about a third of the specimens of basalt are non porphyritic, but these are not necessarily those devoid of olivine. 108 ::\IOLOKAI

Of the porphyritic specimens, most contain phenocrysts of feldspar. Many also contain scattered phenocrysts of olivine, with or without feldspar phenocrysts. Augite phenocrysts, with an optic angle of about 55°, are present in a few rocks. All of the phenocrysts are small, generally less than 2 mm long but rarely up to 3 mm. The feldspar phenocrysts have the same composition as those in the olivine basalts. The groundmass resembles in both composition and texture that of the olivine basalts. In most specimens in which its nature has been determined the pyroxene of the groundmass is pigeonite. In three specimens, how ever, it ranges from augite V{ith an optic angle of about 55° to pigeonite with an optic angle near 0°. In a specimen collected o.n mile S. 33° vv. of Mokio Point the groundmass pyroxene is separable into larger grains with 2V = 45° to 55°, and more numerous smaller grains with 2V near 0°. However, in specimens collected 1.15 miles east of Ka Lae o ka Laau and at the summit of Pun :Nana, such separation is not possible. Equipment to make accurate measure ments was not available, but the gradation in size of optic angle appears to be essentially continuous. HYPERSTHENE-BEARING BASALTS.-Three specimens of basalt con tain rare phenocrysts of hypersthene, up to 2 mm long. These speci mens came respectively from localities: 0.8 mile east of Ka Lae o ka Laau, 2.35 miles S. 70° "\V. of Pohakuloa trig. station, and 200 feet east of Pohakuloa trig. station. The last contains no other pheno· crysts, but both the others contain as well phenocrysts of plagio clase, augite, and olivine. OliYine is present only as phenocrysts, and forms less than 1 percent of the ·rocks. The hypersthene grains are pleochroic from very pale pink to very pale green, and have -2V = 80°. In general they appear to be entirely unresorbed. Hypersthene forms less than 1 percent of the rocks. It is not present in the groundmass, which, in all three specimens, consists of me dium labradorite, monoclinic pyroxene, magnetite, ilmenite, and a little interstitial glass. Hypersthene-bearing basalts have been found also at ,vest Maui Volcano.19 They are fairly common among the lavas of l\1auna Loa, on Hawaii,20 and are predominant among those of the Koolan Yol cano, on Oahu.21

10 Macdonald, G. A., Petrography of Maui: Hawaii Div. of Hydrog., Bull. 7, p. 317, 1942. 20 :Macdonald, G. A., Petrography of the island of Hawaii: U. S. Geol. Survey, Prof. Paper, in press. 21 ,ventwortl1, C. K., and \Vinchell, H., The Koolau volcanic series, Oahu, Hawaii: Geol. Soc. America Bull., vol. 58, pp. 45-77, 1947. PETROGRAPHY 109

QUATERNARY VOLCANIC ROCKS

KALAUPAPA BASALT. The lava of the late eruption whif'.h built Kalaupapa Peninsula, at the foot of the northern cliff, is a dark gray rather mafic olivine basalt pahoehoe, with abundant phenocrysts of feldspar up to 4 mm long, and olivine and augite up to 2 mm long. The olivine has a -2Y close to 90°, and is unaltered except for a faint yellowish stain around the edges. The augite has +2v = 60° and fairly strong inclined dispersion. The plagioclase phenocrysts ar·e zoned from medium bytmvnite to medium labradorite. The groundmass is inter·ser·tal, and consists of medium labradorite, pigeonite, olivine, magnetite, ilmenite, and interstitial glass. The pigeonite is slightly purplish brown, and is probably titanian. The glass is pale brown, and is generally clouded with finely granular iron oxide. The phenocrysts grade in size into the groundmass, and no sharp line can he

MAGMATIC DIFFERENTIATION The lavas of -west Molokai depart little from the composition of the basalt which forms the great bulk of the Hawaiian volcanoe~ and represents the nonvolatile portion of the parent magma of the Hawaiian province. The small amount of differentiation which has taken place is easily accounted for by the sinking of early-formed crystals in the magma column. The large proportion of olivine-poor basalts in the upper part of the West Molokai shield probably repre sents a period during which eruptive fissures tapped only the upper most part of the magma column, from which the olivine phenocrysts had settled out. The lavas of East Molokai, on the other hand, include types 110 MOLOKAI which differ greatly in composition from the parent olivine basalt. Nearly the entire range of Hawaiian lavas is included, among the major types only the nepheline-bearing lavas being unrepresented. The origin of the various lava types is discussed at length else where,22 and space will not be taken here to repeat the discussion. It is sufficient to state that the other types can be derived from olivine basalt very largely by crystal differentiation.

22 Macdonald, G. A., The Hawaiian petrographic province: in preparation. INDEX

PAGE • • • . PAGE Abstract ...... 1-2, 89 D1fferentiat10n, magmatic ...... 109-110 Acidity, of water...... 79 Dike, arched banding of vesicles (fig. 4). 18 Acknowledgments ...... 7 :pike complex, proposed tunnels in 82, 83, 85 Adz rock, quarries...... 25 Dike tunnels, regulation of discharge. . . 86 West Molokai ...... 107 Ahaino Spring ...... 70-71 Airport, test-boring at ...... 61, 63 Dikes, confining ground water...... 72-77 Alexander, W. D. cited...... 53 in face of cliff, view...... plate 4 Alteration, hydrothermal ...... 92 on East Molokai ...... 18-19 American Sugar Co., historical note. . . . 5 on West Moloka.i ...... 25 Analyses, chemical, oligoclase andesites petrography ...... 104 (table) . • • . • • • • ...... 102 Domes, bulbous, on Enst Molokai...... 23 che1:11ical, water (table) ...... : 78 Drilled wells, abandoned (fig. 14)...... 66 Andes!ne andesites, petrography...... 103 records (table) ...... 64-65 Andes1te, oligoclase, petrography...... 99 Dug well 42, fluctuations in water level oligoclase, view ...... plate 15B (fig. 12) ...... 62 Andesite fl.ow, view ...... plate 14A Dug wells, records (table) ...... 58-59 Andrews, Carl, cited...... 53 Dunes, consolidated . . . . . • ...... 28 Armored desert, view ...... plate 6B sand, lithified ...... plates lOA, lOB Augite phenocrysts ••...... , .. 96, 99 unconsolidated ...... 28-29 Augite-rich type of picrite-basalt defined 98 Dunite ...... 104 Anstin, H. A. R., cited ...... 8i, 82, 81., 86 Earthy deposits, consolidated ...... 27-28 Badon Ghyben, W., cited...... 53 unconsolidated ...... 28 ~art~, T ..F. W., cited...... 96 East Molokai Mountain, caldera Basa sprmgs ...... _5 6-5 7 complex ...... 19-22 asa1 water ...... 53-67 extinction ...... 16 future developments ...... 84-87 form ...... 11-13 Basalts, petrography ...... 97-98, 107-108 geologic structure ...... 29-31 Bays ( see under proper name) ground-water conditions (fig. 16). . . . 76 Beach deposits ...... 29 minimum daily discharge of streams Beach rock ...... 27 (table) ...... 77 view ...... plate 9A profiles (fig. 3) ...... 12 Beaches (see under proper name) proposed routes for development of Beef production ...... 5-6 water in (fig. 17)...... 80 Bigelow, L. H., cited...... 8 southern slope, view ...... plate 6A Dlack santl ooacl.tes, occurrence...... 29 strntigrnphic tnble ...... facing page 10 Biotite ...... 97, 101, 105, 107 subareas ...... 11 Block lava, flows resembling ...... 100 view from Kaunakakai wharf ..plate 14B Borings, test (table)...... 55 water-bearing properties of rocks Boulders, rounded by wave action, view 16, 17, 19, 21-22, 23 B . plate 5B East Molokai volcanic series ...... 16-23 readfrmt-tree well ...... 60 lava flows, lower member ...... 16-17 Breccias, in East Molokai Mountain ... 19-21 lava flows, upper member ...... 22-23 in West Molokai Mountain...... 24 oligoclase andesite flow, view...plate 15B Brown, J. S., cited...... 54 petrography ...... 92-104 Rnlbous do~es, on East Molokai stratigraphic section (table) . . . !Hl-!l5 Mountain ...... 23 type locality. lower member...... 16 tYpe locality, upper member...... 22 view from Waialua ...... plate 15B California Packing Corporation, acreage 5 view in east wall of Kamalo Gulch Carson, M. H., cited...... 72 plate 14A Cattle introduction ...... 3 view in head of Kamalo Gulch ..•plate 7 A Cederstrom, D. J., credited...... 6, 89 Edwards, A. B., cited...... 96 Chalcedony ...... , 24, 92 Emerged shore lineR ...... •13-14 Chemical analyses, oligoclase andesites Erosion ...... 12, 13, 35 (table) ...... 102 water (table) ...... 78 Chloritization of lavas ...... 96, 97, 98 Faults. on East Molokai ...... 30-31 Clark, W. 0., cited...... 30 on West Molokai...... 31 Cliffs, sea, on East Molokai, view....plate 4 view ...... plate 12A sea, on West Molokai, view ...... plate 7B Feldspar phenocrysts, alteration of Climat,e •••..•.• , ...... , 1:V{·4'5 . 95, 98, 103 Conant-Kaunakakai well ...... 60, 62 of andes1tes ...... • . . 100 Conant-Kawela well •. , .•...... •57-60 of basalts ...... 95, 106 Cones (see also under proper name) Finch, R. H., cited. . • ...... • 100 on East Molokai ...... 17, 23 First Progress Report, Haw. Terr. Plan. on West Molokai...... , 24·2G Bd., cited ...... 4, 49 Coral reef, fringing, view ...... plate 6A Couthouy, Joseph P., cited...... 14 Cross, W., cited...... 91 Gabbro ...... 104 Geologic development (fig. 5) ...... 32-33 Geologic guide to ronds ...... plate 2 Dana, J, D., cited...... • 7 Geologic history ...... 31-35 Deer, W. A., cited...... 95 Geologic map of Molokai ...... plate 1 Deposits. beach ...... 29 Geomorphic areas of Molokai ( fig. 2) . . . 1O calcareous marine ...... 26-27 Geomorphology ...... 11-35 consolidated earthy ...... 27-28 Ghyben-Herzberg principle, discussion .. 53-54 unconsolidated earthy ...... 29 illustrated (fig. 11) ...... 53 Development, geologic (fig. 5) ...... 32·33 Graben, view ...... plate 12A 111 112 INDEX

PAGE PAGE GraYcl terrace, view ...... plate OB Living rec£, presence of ...... 1:. Ground water, acidity (table)...... 79 Loiloa Spring ...... 56 areas (fig. 15) ...... 68 chemical analyses (table)...... 78 confined by dikes ...... 72-77 Macdonald, G. A., cited future developments ...... 84-87 13, 78, 96, 98, 99, 101, 103, 104, 108, 110 perched ...... 67-72 Magmatic differentiation ...... 109-110 quality of ...... 77-79 Mahana graben, view...... plate 12A section showing conditions (fig. 16) . . 76 Malihini Cave, spring near...... 71 use from large windward valleys .... 79-84 Mapulehu, wells at ...... 55, 59, 60 Groundmass. of olivine basalts...... 97 Marine deposits, calcareous ...... 26-27 Maui-type well 1, fluctuations in water level (fig. 12) ...... 62 Halawa Stream, intensity-frequency Maui-type well 6, fluctuations in water curve (fig. 9) ...... 49 level (fig. 13) ...... 63 Halawa Valley, aerial view ...... plate 11 Maui-type wells (table) ...... 60 Haleloulu Spring ...... 70 1.feinzer, 0. E., cited...... 5i: Hanalilolilo hill, composition...... 23 Meyer Lake ...... 49-50 Haupu Bay, fault at...... 30 view ...... plate 12B Haupu Bay mass, composition...... 21 Mineralization, secondary ...... 19, 9'.! Herzberg, Baurat, cited...... 53 Mohle, F., cited...... 90 Himh,, N. E. A., citeu...... 8 Mokuhooniki cone, geology of...... 26 History of investigation ...... 6-7 petrography ...... 109 Hone~ production...... 5 Molokai, aerial view from the east. . plate 3 Hoolehua Plain, origin...... 13 area ...... 3 Hornblende ...... 101. 105 climate ...... 37-46 Howe!, Hugh, cited ...... 6, 8, 81 geologic u.eveluprneuL (fig. 5) ...... , 32-33 Humidity . , ...... 37 geologic history ...... 31-35 Hypersthene-bearing basalts ...... 108 geologic and topographic map .....plate 1 geomorphic areas (fig. 2) ...... 10 geomorphology ...... 11-3i> Inclusions, in lavas...... 104 ground-water areas (fig. 15)...... 68 Iddingsite, origin of ...... 96, 107 ground-water conditions (fig. 16) . . . . 76 Industries of Molokai...... 5-6 historical sketch ...... 3-5 Intensity-frequency curve, Halawa industries ...... 5-6 Stream (fig. 9)...... 49 ]and utilization in 1937 ( fig. 1) . . . . . 4 Tntroihrntion . . . 3-9, 89-90 mean monthly and annual Intrusive rocks (see under Rocks) temperatures (table) ...... 38 Iwashita, S., chemical analysis by ..... 102 petrography ...... 89-110 credited ...... 89 population ...... 5 rainfall ...... 3 7 -46 John Kupa well...... 60 road guide ...... plate 2 ,Jorgensen, J., cited...... 81 water supplies (fig. 10) ...... 51, 52 Judd, G. P. IV, cited...... 3 Molokai Ranch, Ltd., acreage...... 5 Montmorillonite ...... 24 Moomomi Beach ...... 28-29 Kua cu11e • • • ...... • 25 distant view ...... plate 7B Kahananui Stream, spring on...... 70 Ocean water, chemical analyses (table). 78 Kalaupapa basalt, description ...... 25-26 Ohialele Stream, view ...... plate 13B petrography ...... 109 Ohrt, Frederick, cited...... 80 Kalaupapa Peninsula, view .....plates 4, SA Oligoclase, potassic ...... 101, 102 Kamalo gulch, view ...... plate 7 A Oligoclase andesite, chemical analysis. . . 102 view of east wall...... plate 14A petrography ...... 99-lOg Kamalo well ...... 58, 62 view of flow ...... plate 15B Kamiloloa intake, spring near...... 69 Olivine basalts, petrography .. 95-97, 105-107 Kanewai cone ...... 2d Olivine phenocrysts, of hasalts .. 95, 99, 106 Kanoa well ...... 60 Ustergaard, J. J\I., cited ...... 8, 26 Kapuna Spring ...... 67-69 Kapuna Stream, daily discharge (table) 69 Kauhako Crater, view...... plate 4 Papalaua Valley, view ...... plate 13A Kanlahnki hill, r.omposition . . . . . 28 Pegmatitoid ...... 107 Kaunakakai, test borings near ...... 55, 66 Pelekunu Bay, unusual u.ike (al;,u Kaunakakai Gulch, springs on ...... 69, 84 fig. 4) ...... 18-19 Kaunakakai shaft ...... 6, 57 Pelekunu Stream, duration-discharge Kawela, basal springs at...... 56 curves (fig. 8)...... 48 composition of well water at...... 78 minimum daily discharge (table). . . . . 77 Kokokahi, spring at...... 56 Pelekunu Valley, dikes in...... 18 Keawanui fishpond, spring at...... 56 origin ...... 11-13 Kualapuu, drilled well at...... 61 springs in ...... 71, 75 view ...... plate 5A Penguin Bank ...... 14 Land utilization in 1087 (fig. 1) ...... 4 Perched ground water ...... 67-7? Lanipuni Stream, minimum daily Perched springs ...... 67-71 discharge (table) ...... 77 Perched water ...... 49, 50 Late lavas, West Molokai (fig. 18) .. 105, 106 future developments ...... 84-87 Libby, McNeill, & Libby, acreage...... 5 tunnels driven for (table) ...... 73 well on West Molokai...... 61, 64, 74 Perennial streams, permanence of...... 47 Limestone, reef, of W aimanalo stand of Petrography ...... 89-110 sea, view ...... plate SB Picrite-basalt, types of, defined...... 98 Lindgren, W., cited...... 7, 53, 71, 79, 91 Picrite-basalts, petrography ...... 97-98, 107 Lithified beach sandstone, view ....plate 9A Pineapple production ...... 5-6 Lithified sand dunes. view...plate lOA. lOB Pleistocene shore lines on Molokai (table) 13 Livestock, production ...... 5-6 Potassic oligoclase ...... 101, 102 INDEX 113

PAGE PAGE Powers, H. A .. cited...... 99 Tunnels, driven for perched water Powers, S., cited...... 9, 91, 103 (table) ...... : : . . . 73 Precipitation ...... 3 7 -,6 proposed, in dike complex..... ti.:, ti3, 85 Primitive type of picrite-basalt, defined. 98 proposed routes (fig. 17) ...... 80 Pseudomorphs, after amphibole ....101, 103 yielding perched water ...... 71, 74 Fulena Stream, duration-discharge Type locality, East Molokai volcanic curves (fig. 8) ...... 48 series ...... 16, 22 minimum daily discharge (table). . . . 77 Puu Kaeo, composition...... 23 Puu o Kaiaka, description ...... 24-25 Ualapue well ...... 60, 63 Puuohoku Ranch, acreage...... 5 Unconformity ...... - ...... 23 Pyroxene, trend of crystallization in .. 96, 108 U. S. Geologieal Survey, "\Yater-Supply papers cited ...... •.48, 59, 66 Rainfall ...... 37-46 annual (table) ...... 43-46 areal distribution and location of rain Yaksvik, K. N., cited.. 27, 53, 57, 78, 86, 92 gages (fig. 6)...... 39 Valleys ( see under proper name) average monthly distribution ( fig. 7) . 41 Volcanic series (East·Molokai, West Mo- highest recorded ...... 40 lokai) (see under proper name) lowest recorded ...... 40 Vesicles, arched banding of ( fig. 4) . . . . 18 mean monthly and annual records (table) ...... 42-44 Ranches, acreage ...... 5 Wager, L. R., cited ...... 95 Reef limestone, of \Vaimanalo stand of Waiakeakua Stream, mininmrn daily dib sea, view •...... plate 8B charge (table) ...... 77 Riebeckite-like mineral ...... _. _ 100 Waialala, springs and tunnels ut •• 50, 67, 71 Road metal ...... 35 springs and tunnels at, daily discharge Rocks, general character and age ..... 15-16 (table) ...... 72 intrusive, on East Molokai ...... 17-18 Waiauni Spring ...... 67 intrusive, petrography ...... 104-105 W aiele cone, fl.ow from ...... 24 petrographic classification ...... 90 \Vaihuna hill, view...... plate 12A Quaternary volcanic ...... 25-26 Waikolu Stream, minimum daily Quaternary volcanic, petrography. . . . 109 discharge (table) ...... 77 sedimentary ...... 26-29 ·waikolu Valley, dikes in...... 18 stratigraphic table of Molokai springs in ...... 75 facing page 16 \Vailan V nlley, origi11 . 11-1 R Tertiary volcanic ...... I.o-2!) springs in ...... 71, 75 Tertiary volcanic, petrography .....92-108 stocks in ...... 17 water-bearing properties, East Molokai \Vater (see Basal water, Ground water, 16, 17, 19. 21-22, 23 Perched water, Surface water) water-bearing properties, West Molokai ·water development, proposed tunnel 16, 21, 25, 26, 28 routes (fig. 17) ...... 80 unpublished reports relating to...... 8-9 Sand dunes, lithified, view ..plates lOA, lOB \Vater supplies, sources and pipe lines Sandstone, lithified beach, view ....plate 9A supplying (fig. 10)...... 51 Sea cliff, East Molokai, view ...... plate 1 towns and villairns (table)...... 52 West Molokai, view...... plate 7B Wave action, on boulders ...... plate 5B Sedimentary rocks ...... 26-29 producing armored desert ...... plate 6B Shore lines, emerged and submerged ... 13-14 ·wen water, chemical analyses (table).. 78 Springs (see also under proper name) \Vells, ...... 57-67 basal ...... 56-57 drilled (table) ...... 64-65 perched ...... 67-71 drilled, abandoned (fig·. 14) ...... 66 Stearns,H.T.,cited.. 8, 12, 13, 14, 26, 27, dug (table) ...... 58-59 30, 31, 53, 57, 78, 82, 86, 92 graphs showing fluctuation of water Stewart, J. E ., cited...... 8 level in (figs. 12 and 13) ...... 62-63 Stocks, occurrence ...... 1 7 Maui-type (table) ...... 60 Stratigraphic table of Molokai. facing page 16 Wentworth, U. K., cited 8, 8, 58, 54, 67, 108 Submerged shore lines .. , , .. , , .... , .13-14 West Molokai Mountain, extinction..... 15 Sugi, K., cited...... 102 geologic structure ...... 31 Surface w.ater ...... 47-50 late lavas of...... 105, 106 acidity (table) ...... 79 position of late lava flows (fig. 18). . . 106 future developments ...... 84-87 stratigraphic table ...... facing page Hi use, from large windwa1·d valleys .... 79-84 subareas ...... • 11 Swartz, J. H.,. cited...... 8 view ...... plate 6A view of ea;;tern slope ...... plate 12A view of sea cliff on northern coast. plate 7B Tompcrnturc ...... 37 water-bearing propertie:s of rock,; ...10, 21, mean monthly and annual (table). . . 38 25, 26, 28 Terrace, gravel, view...... plate 9B West Molokai volcanic series ...... 15, 23-25 Test borings, records (table)...... 55 petrography ...... 105-109 Trachytes, petrography...... 103-104 view near Halena ...... plate 15A 'l'nff i!PpoisitR. on East Molokai...... 17 Winchell, H., citod...... 10S on West Molokai ...... , 24-25 Wind ...... 37